I want a split receiver but top and bottom wise would be way better if that could be worked out. I mean im not sure if it could be but I think that would make cleaning it a lot easier, its such a PITA atm.
A lever changer would be cool but not required.
Lose the finger grooves for sure. Add the ability to add .45grips?
In a new receiver the ability to add real gun sights would be nice too.