I disagree on your point about USF losing flexibility due to teching nades. It gives you smoke + grenades, that makes your rifles alot more flexible depending on the situation. I know you meant faction, but rifles are a big part of it.
The other thing is, don't play your opponents game, if he jumps in a building and you keep attacking it and fail at countering, then you are doing it wrong. Make yourself unpredictable, do things that make him question if keeping 1 necessary unit in a building or not. I have a replay on Semoskiy, where my opponent wires my bridge and puts an mg in the building, I just put my focus on him catching me, eventually getting the cutoff point back.
In addition I would prefer for each unit to have a time to get out just like MGs. The instant hopping is simply stupid.
This is a great change I feel.
The problem against good players is that grenades are not a reliable counter to garrisoned units, they are too easy to dodge. This change would help grenades in that department, as well as help reduce the pervasiveness of garrison play these days.