Consider the bunnyhopping ability in taxis useless, it was crap in SA, it can only get crappier.
I dont think you can make that assumption, GTAIV runs on RAGE which is completely different to the engine that ran 3, VC and SA so we have no idea how the physics will work or what glitches will exist, we might need to reconfigure how stunts we do today are performed to make GTAIV workable
I enjoyed the trailer Things I noticed
-A side mirror in the car that works
-The white cop car looks nice
-The graphics are fucking awesome See the detail with the door getting kicked in!
-THERE WAS A MOTORBIKE!!!!!!!!!!!
-Awesome looking Hunter
-Holding onto the back of a truck and a helicopter, if that could be done in game...imagine some possible stunt abilities in parkour stuff
-Basketball courts are back (B-ball 2 )
-Windshield damage...hard to say from the trailer but if it is dynamic that is pretty cool
-I saw a Binco, that might mean my Green Eris t-shirt may make a return
-Some nice terrain, I spotted a couple of random stunt spots
Awesome trailer, action packed