If you like the idea to build certain ships on certain planets only, I recommend you the Balance and Flavor submod from Vulcanus.
It's also a thing in 2.2, and to a smaller extent was also a thing in 2.1
Thanks for the suggestions Raw. A few points of feedback:
Even though there was a bit of overlap in-universe as far as who used what, you need to look at it proportionally, how those factions tended to come by those units, and also what the goal of a unit roster is. For the first bit, yes, there are a few examples of different groups, like the New Republic, using Imperial Star Destroyers. This was not, however, because they produced them; they had them in small numbers because there were some they had captured. We also know that even when they did capture Kuat, Bilbringi, Fondor and so on, which were Imperial shipyards, they were not used to produce more ISDs for use by the New Republic; they produced their own variants (the Nebula, Republic, and Endurance, for example, and it's also not correct that Mon Calamari was the only planet that produced the dedicated Mon Cal warships; in-universe starship production is a lot more specific and specialized than it's worth representing in the mod (otherwise you'd only have like 5 planets that can produce any ships whatsoever), but youd still see other New Republic shipyards building or at least outfitting Mon Calamari designs for the New Republic. Case in point, the ships that were being either fitted or refitted at Sluis Van which were jacked by Thrawn. And when the New Republic military philosophies did start becoming more similar to the Imperial ones and they wanted to build their own superships, they didn't build more Executors, even though they had captured both Lusankya and the planets which were typically used to build the Executor-class under the Empire; they instead contracted it to Mon Calamari to build the Viscount and the Mediator. We also know what it looks like when Mon Calamari falls under Imperial control; they didn't build Mon Calamari warships for the Empire; they actually built nothing, because the Mon Cal and Quarren were uncooperative until they were working for a government they supported, and ay attempts to adapt their tech failed. Ingame we have to use a more generalised system though, so a shipyard is a shipyard.. Pre-Clone Wars they built the Rendili Stardrives Dreadnaught design, though, for a government they did support even though it wasn't a native design, and during the Clone Wars some exiled Dac shipwrights also designed and built the Providence for the government they supported, not for the Republic when they controlled the planet. So, simply controlling a planet didn't determine what ships a government used. You can certainly make the argument that without Mon Calamari those ship types wouldn't have been in the New Republic's arsenal, but the engineers and tech still existed , other shipyards could make it with those engineers, and more important than Mon Calamari just being part of the New Republic was that the New Republic was probably the only government with whom the Mon Calamari would cooperate in the same way. The "Imperial" shipyards were typically a bit more pragmatic, but their output was still tailored towards their contractors. Much the same as if, say, any given group in WWII had taken over the means of production in another country; just being in Germany doesn't necessarily mean Russians would have built Tigers and Panzers.
Yes, theirs some designs like the Nebulon-B which began as Imperial ones and saw limited use under the Empire, however we're trying to represent what would most likely be found within a faction. So while, yes, you could say an Imperial shipyard could build Nebulon-Bs as it was an Imperial government design, they were far more common within the Rebellion and the New Republic, and exceedingly rare within the Empire; there are almost a dozen better purely-Imperial alternatives to use, and we don't want to clog up the build bar with redundancies; it's almost full for each faction as it is, and those redundancies add nothing to gameplay. Ultimately we're choosing the options which best reflect those factions. For an Imperial group like Zsinj, where they were far more common, it makes more sense for us to use the Nebulon-B in his roster, so we have done so. While there were a few planets where Clone Wars holdovers were used as garrison forces (they were almost never produced again by those Imperial groups mind you, they were just laying around), it makes sense to use them within the Pentastar Alignment because of where they are based; the Outer Rim had most of those holdovers, so it gives a better sense of who they are and what their roots are as a faction to use the Clone Wars holdovers. We're trying, again, to not just represent every ship type of which the faction may have had an example, we're trying to extract the essence of what they faction is and represent it ingame through the unit lists. Factions didn't just make their rosters based on whom they controlled and just use whatever native ships were available, nor did every ship type they used necessarily represent what could typically be found within said faction's fleet or what that faction stood for, and that's the bigger goal when deciding what a faction can or can't build within the context of the mod.
1) Make the class of station mater what you can build, like a level 1 Frigates can only build light frigates, a level 2 station can build heavy and light frigates, and a level 3 station can only build Capital Ships, making them more important to keep several in service.
This doesn't really make sense either from a gameplay or in-universe perspective, and it sort of contradicts your previous points as well. In-universe, those ships were all made by the same companies at the same planets (hence the contradiction), and from a gameplay perspective, this could potentially get a bit frustrating. The biggest example, I guess, is FTGU; you only have one planet, and it tends to be a heavy frigate shipyard planet to start. Since you have a heavy frigate shipyard, this would mean you're not allowed to make light frigate shipyards at alll, even though your planets clearly have the infrastructure to do so. Or a lot of other GCs where factions only have one planet in a given area, which is especially common for the New Republic, which usually has Mon Calamari pretty isolated. The only thing they could build there would be capital ships, and they'd have no planets around them to use to build smaller ships and help to expand. Plus, this would mean you have to take the shipyards out of the upgradeable slot, since you can't make them only have access to one tier. You'd also have to limit it to one special structure slot per planet so they can't build the other possible levels as well.
2) Adding criminal factions that start small but can become a big faction with similar mechanics with Force Corruption. Basically add Zann Consortium, Hutts, Black Suns, and so on that can make it difficult and either to hunted down or force away with bribe money.
The Zann Consortium and Black Sun were basically non-factors in the galaxy at this point; most criminal organizations only had like one or two secret bases, and never really would have had ships to challenge anyone else. We also have next to no faction slots to work with, and new factions take a considerable amount of resources to make. The Hutts are a possibility we've considered in some form, although we'd really be fudging their capabilities and political structure to make them a faction, really.
3) The Madalorian Faction as a minor faction with ships and forces similar to Zann Consortium, Imperial Remanent and New Republic, a Separatist Rogue Droids with clone era Separatist Droids.
Mandalorians were essentially nothing at this point. They had no navy to speak of, and the only active ones were pretty much just bounty hunters. The last time they'd had the capability to field any sort of significant military force had been a long time ago, and the next time they'd even be a significant part of a military coalition (not even on their own) would be the Confederacy led by Corellia several decades after the mod ends. Even then it was primarily just fighters that they provided. Separatist holdouts were pretty much, if not completely non-existant at this point. Leftover military hardware had either been sold off to groups like the Corporate Sector Authority and integrated into other people's forces (ie how we've given Zsinj access to Lucrehulks and Droideka, PA access to Munificents, and the Maldrood access to Providences) where possible/reasonable, or just been destroyed.
4) Add two more eras: A 0 era as playing as the Rebel Alliance before it became the New Republic to feel like your building from the ground up, and Era 6 during the Young Vong Invasion with the Young Vong invading starting with a random world in the outer rim. Hint, will be weakest defended world leads to a automatic defeat for which ever faction holds it.
These both honestly would constistute pretty significant additions (for the first bit) or overhauls (for the second) to the mod. Initially for 2.2 we were going to do a pre-Endor GCW scenario instead of the Warlords, but ultimately we decided to focus on improving and fleshing out what we have within the existing (and already pretty expansive) scope of the mod, rather than diluting it and adding on more stuff to an already hefty package. If we were to tackle the Vong, Ascendancy is a much better venue for us to do so.
Forgot to add, would like the ability to build civilian spaceports that work on a similar fashion of mining stations but design to build up trade.
We are doing some more types of space structures, including trade ports.