I feel that it is waaayyyyyy to soon to reboot Buffy. Save that for sometime in the next decade. This is the kinda crap that makes me hate studio's.
With that being said, Kristen Bell should play Buffy in a reboot, with Ben McKenzie as my early choice for Angel. Not as tall, but he can nail the character.
They could always just make a movie about ANOTHER Slayer.
This brings up a question I have for die hard Whedonverse fans. Was there ever any episodes involving Shifters? I know there wasn't in Angel, but I forget if Shifters were used in Buffy. They used every other type of supernatural being, but I can't remember any shifters. I'm trying to come up with my own Whedonverse fanfic, which I have stalled on multiple times, and I would like to have one of my main characters be a shifter.