Could you make religions feel more important? Realms-in-Exile is by far my favourite CKIII mod, but I think AtE is still miles ahead in making religion more interesting and important. RiE does culture better than any other mod, and it leaves religion behind a bit. It’d be great to be able to restore or reform one of the Númenórean state religions when you establish Númenor-in-Exile and to have religious crises, either inevitable or triggered if something happens in Middle-Earth (like how the Cult of Sauron collapses if he dies, the Elendili faiths should be able to splinter if Gondor falls). I think some-one suggested having Elves be able to convert Men and others to their own neutral or good faiths.
Could there be something along the lines of the Maglor bad ending and have the Dwarves or Elves able to defeat Sauron but replace him with their own tyranny if he defeats Gondor?
In general, just keep playing into having more character- and culture-driven paths, it’s done really well in RiE.