XP modifier would be nice to have now that we have custom difficulty and you already have system for that in place too with INT effecting xp gain on classic and xp needed on oddity.
My reasoning for that is that on higher difficulties, especially dom, there's generally a lot more enemies and also higher tier ones much earlier as well, like burrower warrior which normally you only get to see in DC on normal (veteran) but on dom you can find a few as soon as before even doing outposts. So basically it allows you to get rare enemy oddities much earlier. So to balance that you could lower xp modifier to compensate for larger amount of xp you gain early and more. On opposite side, another reason is that some people just may like to try out some weird builds and some of them only get going at really late levels (like riot shields which need all the feats and spec points they can get) by which point there's barely anything left to fight. With high enough modifier maybe even meme lvl 50 is something feasible to reach without endless tchortling grind.
Also, I'm not sure it even has any actual effect on enemy stats but if it does then NPC level modifier to allow to increase their levels would be pretty neat too.
