As a first step, I'd consolidate the lore in the past so it makes more sense. Like give Gallia a better reason to be the way it is than "they're still angry at something that happened 800 years ago so they launch a genocidal total war". Undoing bad and illogical stuff by erasing them form history is absolutely an option (re-writing gallic history, changing "the wilde" to something like "the infested" or "the enlightened", re-defining or properly defining what a nomad actually is), or the mod will only get worse with time.
Then, I'd make knowledge of the storyline and lore more accessible ingame, so people will even know and start to care about it.
When that's done, I'd look what's happening in player's RP and incorporate the parts that are logical and conductive to good game play (that does NOT include "my faction stronk so all your base are belong to us now").
When something is identified as good, I'd invite the people who did it to incorporate it into the storyline, in a non self-aggrandizing advantage-seeking manner.
I'd work with system developers so that activity hubs (places where trade routes, repping missions, mining locations, military conflicts, and natural travel paths coincide) deliver part of the story to players.
