I think that it is clear now that this is unlikely to happen. Bannerlord is built on 4 gameplay pillars:
Action > Simulation > Tactical > Roleplaying
And the importance of those pillars are in that order. The way I see it the quest and dialogue system is there more as a example for modders.
TW nailed the action pillar and they have been mostly working on the simulation pillar since Early Access began. I expect there is some tactical work still coming since sieges need fixing and battle commands are getting some love.
This doesn't leave a lot of time left for the Roleplaying pillar apart from competing the main quest line. Actually calling it main quest line implies there other quest lines, which is inaccurate.
I have made peace with it, and now actually think it is for the best. They have limited resources and adding more RP content to the world is probably one of the easier type of mods to create, I just wish the world lore was more fleshed out so we would have something to anchor story mods to.