I think they're going to be incredibly lazy about implementing this at low levels. In fact, I expect zero changes.
There's no resilience gear, the odd blue item in BC non-heroics excepted, before 70. There's no mastery gear on LK gear and even the 77-79 cata greens that have it don't benefit a player until they train for it at 80. I'm expecting this to be an 85-90 stat. Otherwise they're going to have to re-itemize 3 expansions of resilience gear. They're too lazy. We all know this to be true.
I think the ridiculously simplistic talent trees are going to negate the sometimes absurd burst in this bracket but it won't be the gear that makes the difference. Hopefully it will make less viable classes viable. However I don't expect this to really change how 70's gear too much. Sure you may not have rogues (Yes, I have a BIS Sunwell/glaives one.) stacking 20 agi in every slot but I don't expect anything more dramatic than having to regem. After all, I made a 560-600 resilience resto shammy with 3 pieces of PVE gear. It can be done.