Will be interesting to see how much it is. It's a nice change.
Spell Reflect is being changed to a 25s cooldown, though, which makes it quite difficult to use now. But the Shield Block change seems like a better trade-off.
I'm not totally sure why it's being put on Shield Mastery though--that's already a required talent with its current effects. Should be a Protection spec passive. (Not that it really makes much difference, just a point of principle really. :P)