Regicide is something I'd still like to try to do but by necessity, the era system is pretty much the definition of spaghetti coding and it would be very easy to break it in a frustrating way, so I've been holding off on it until the dust settles on more other stuff to even try it.
You could do like a historic battle to get rid of it i.e. win at bilbringi and lose thrawn and inorder to not skip a stage have each planet locked till that era similar to byss.
This tend to not work in a sandbox mode, especially in one where there's so many different ways for things to potentially play out. There's any combination of 9 different factions to take into account, and having historical battles like that depends on the right faction controlling the right planet at the right time to even potentially happen, and considering story scripting can
ONLY be done with the first three factions (IR, EotH, NR) it's only even remotely possible in GCs where the player is playing as those factions. But, say by Era 2 the Pentastar Alignment, Duskhan League, Hapans, Hand, Maldrood or Eriadu control Bilbringi. Or say the Remnant does, and it's only of the other 7 that attacks instead of the NR. Or the NR heroes that would have been at that battle canonically (and therefore be there if we made it a scripted event) were dead and not there. There's no way we could make events like that happen and make sense without the correct heroes/factions being at the right place already, in which case why even bother scripting it?
This is why historical battles, if they were to be attempted, would be a much better skirmish thing. It's also why we've only tried to do heavily scripted missions/events in the GC with only two active factions (two of the three that can get story scripting), and it has to be events that could occur independent of player actions- the Battle of Bilbringi was the Battle of Bilbringi because that's where those people had that engagement, and that's where Thrawn ultimately died. The Katana Fleet would have been there regardless. In any given GC, any player could have their own "Battle of Bilbringi" (in terms of what made that engagement special) pretty much anywhere, like Coruscant or even somewhere really special like Polneye.