From blizzcon:
Q: Shadow Priest's Dispersion is lackluster. Any chance for some buffs?
A: Probably not. The Devs are happy with the way it is. It's a partial shield that does not root you. Yeah it's not terribly useful for high-end PvE, but it is beneficial in other way and 51-Point talents are often very situational.
The devs obviously don't know how to develop classes as this is the worst 51 pt ever yet they still refuse to buff it.
I really wan't blizzard to fire those stupid devs and get some ones that can actually do their job.