- A full, detailed inner game time, complete with day/night cycles for all planets and locations, and weather differences wherever it makes sense. Also seasonal variation if the game goes on long enough and takes place in such locations that the seasons should change.
- Optional katana or similar-looking sword for Shepard, in place of one of the back-mounted ranged weapons - and some melee attacks to go along with it. I've wished for this for every ME game, but it just doesn't seem to happen.
- Random "interact-with-the-environment" functions that increase immersion, like being able to sit down on chairs, jump, climb trees if you happen to be on a lush garden world, take showers, lie down in the grass or on a bed, etc.
- Being able to reply to your mails and have different storyline outcomes depending on what tone you type in.
- Hand-to-hand sparring with teammates on the Normandy (or equivalent home base) where you can do things like learn some neat moves from Thane (if he's still around) or see if you can beat Wrex without your weapons.
- Male Shepard should get stubble and then a beard unless you shave now and then.
- As was once planned for ME1, yours and your team mates' armour should gradually get dirtier and dirtier as you use it in combat, until you clean it.
- Seamless, loading-time-less zooming from space into the orbit of a planet, and then down through the atmosphere and clouds and down onto the planetary surface.
- Some acrobatic dodges and somersault moves for Shepard, for in-combat use.
I can think of a lot more stuff I'd like to see, but most of it is probably somewhat more likely than 1% to actually end up in the game. 8)