I agree that destructable environments would be a nice feature, but I also have doubts as to weather or not the PPU can deliver. It has thus far failed to live to up any of it's expectations. Some people blame the card itself, others say it's a support issue. Whatever the reason, it hasn't delivered and somehow I doubt UT will be "the game" that makes the PPU shine.
I don't think it will be either. I think physics in games will take several more years to evolve to any level of realism. Destructable environments are only part of what better physics can bring us.