One is working with the current storyline. In my opinion, this would require a hefty amount of cooperation between the various kusari factions, to organise activity, events and such. I've suggested incorporating the kusari unlawfuls into the Kusari governmental body in the past, and I'll do so again. Doing so allows the lawfuls and unlawfuls to work together to provide fair encounters and such.
Second option is adding a war. Going to a war with Gallia seems silly in my opinion, since the reason Kusari stopped the war and was humiliated was their massive defeat at their hands. They wouldn't be eager for a repeat. Besides, practically, only reason Bretonia is holding on is that Leeds has been fortified for years. Kusari has no such fortifications built on their end.
I'd think that Kusari would likely attempt to build defenses in the systems adjoining the Taus, since when you have an imperialist warmonger neighbour intent on conquest, war is a question of when, not if. They'd likely want to expand into the Sigmas to tap into it's resources.
This can be done either with the GMG or against the GMG. They can either agree that cooperation is necessary in face of the Gallia threat, or fight each other.
Either way, expanding into the Sigmas brings one of the largest playerbases into play. the Outcasts. This will do good things to Kusari, and inject activity. Provided you can rope the various Outcast groups in, it'd be even better.