I think something especially nice would be the ability to save per-car FFB values like a number of other sims have. It would solve/workaround the variation in mods at least until some sort of standard is, well, standard. In addition I'd love to see a way to change the FFB strength with finer granularity, as < and > are locked to steps of 5. This is significant when the most I generally have it set to is 30 with my wheel setup, and especially so since as BlueFlame alluded to some vehicles have frankly insane FFB where even a value of 5 may be too high to enjoy, and having to back out to the options menu for a fine adjustment can make mod testing tedious.
As for power steering, it's something I've been trying to figure out since I prefer slower, friendlier road cars over grippy, tight, and altogether "physical" track cars and haven't been able to replicate a nicely self-centering steering wheel (particularly at lower speeds) like in my daily drivers. It's made me wonder if it's in LFS at all, or if so, if it's not speed-variable power assist. Overall I'd say having more tuning options for the handling of cars on a per-mod basis is fairly significant, on both the creator's side and the player's.