I think random encounters on rest might be something Allofich / R.D. has in mind. He might be able to confirm if this is still open.
Yeah, this, or more specifically random encounters in general, are something I mean to put in when I can, but I've been sidetracked.
Crime is another thing that I figured out quite a bit about (like the reputation threshold for when guards kill you versus arrest you, the formula for dark brotherhood or thieves guild bribing the courtroom, etc.). If you worked on that I would like it if you would allow me to come in later and replace/rearrange things as needed to get it to match classic behavior more exactly.
Character generation questions, biography creation/import, and custom character creation are perhaps good ideas if you want to work on implementing something. It seems like we out to already have those in, and they're mostly straightforward I think. I may be able to help there. A while ago I found out the weapon that each character class starts with (in addition to whatever items they get through biography questions), so I could give you that.
I kind of think, though, that with so many features being added, DF Unity could benefit from having some polishing and bug-fixing done to existing features. For example I added climbing recently but it doesn't work yet for climbing out of the water. I don't know much about Unity, I've been focusing mostly on trying to figure out the original game, but I used a check for collision flags to get when the player has been pushing against the wall to start climbing, and this works while out of the water but not while in it for some reason. I know Interkarma is planning to give the PlayerMotor an overhaul but it couldn't hurt to get things functioning properly now, which could be helpful to refer to later.
That's just an example. Another idea is trying to fix incorrect music sometimes playing when loading a saved game (like outdoor music playing when you're in an interior) and things like that. Just my opinion of course.