I really don't see alot to like with the primes. The 24-105mm f/4 IS is almost as cheap as 1 of those and is WAY better built with tons of flexibility with only 1 stop of light lost. Plus canon already has a 17-55mm f/2.8 IS for cropped bodies. A 24-70mm f/2.8 IS full frame model would make these lenses useless and thus i'm curious to see the results of the new Tamron 24-70mm f/2.8 stabilized for this reason. Maybe canon avoided this lens so it didn't hurt their new IS primes. Most video is MF anyway thus the Tamron might be perfect, even if it suffers at focusing.
The 24-70mm f/2.8 needs to be the best lens ever made to compete. Without IS, there will be less love from video users and alot of people already use the version 1 or the 24-105mm f/4 IS. Those that don't will be further swayed by the new Tamron 24-70mm f/2.8 stabilized.