Basically, for PvP defense to be compelling at all, it is going to end up causing the exact same problem Resilience does right now. Taking 28.5% less damage than an entry level player isn't a whole lot less than what we have now, and simply will not have the desired effect at later points in the expansion.
The entire PvP defense idea needs to go... it won't work well just like Resilience doesn't work well. It's effectively the same thing, though ever so slightly nerfed?
PvP gear, I think, really needs to be determined exclusively by PvP power, and player scaling in general just being less extreme than it was in Cataclysm. If, to do that, base player defense needs to be upped to 40 or 50%, or adjusted as time goes by in MoP, that's probably a much better solution than just having Resilience and all of its problems with a different tag attached.
If the problem then is that PvP gear has LESS survivability than PvE gear because of having lower stamina due to the lower item level, it should be pretty easy to adjust the stamina/armor values on PvP gear to be in line with the higher item level PvE gear, no? Especially with PvP power being a "free" stat?
Or how about a set bonus that brings their total stamina and armor in line with PvE gear?