With one side of the conflict completely gone from the game, I think the question of whether the Kusari civil war has a future has been answered already. It's sad, but that's the fact, isn't it?
For me, I think Option 1 (backstab Gallia in Taus) would be preferrable, as it somehow fits to how I imagine a proud Kusari Samura controlled traditional empire that was humiliated by the Gallic roll-over.
Option 2 (fighting Liberty on Gallia's behalf) would create a lot more activity and would likely be a better source of activity and pews for Kusari. RP justification would be that a Kishiro Kusari is just too weak to say "no!" to anything Gallia orders them to do. They could use skirmishing techniques to bind LN forces from moving to Magellan/California, and thus avoid any full-out counterattacks that would wreck Kusari's weakened fleet.
I agree that every House needs a full blown war.
It's sad to see the nice storyline of the civil war fail, but I think it would be somewhat naive to still believe that this will become a thing again. I'll happily let myself be proven wrong on this, though!
