This is an issue that I had hoped would not become a problem due to Blizz keeping item budget under control in Cata (as compared to Wrath adding unanticipated ilvl inflation to accomidate hardmode changes mid-stream).
Basically any current raiding paladin using correct gear choices can trivially achieve full CTC in 378 Firelands gear (and even easier with some heroic gear), while still even using a stamina trinket and matching socket bonuses (i.e. not going full 40 Mastery indiscriminately).
In 4.3, from the looks of the current itemization on the PTR, it will be even more trivial to achieve full CTC, to the point where paladins will start to need to reforge out of Mastery in order to avert completely worthless additional block over full-CTC. That being the case, we will see a situation where paladins will no longer be able to actually benefit from Mastery scaling on gear, and will only improve their survivability from gear by adding avoidance (which is strictly inferior, both in the sense that it is hindered by dimishing returns, and that it provides less average damage reduction per point in any sort of average damage reduction analysis).
Should we be concerned that Blizzard hasn't addressed the fact that Paladin tanks will no longer scale with Mastery from gear in the final tier, while all the other tank classes will continue to?
I concede it's totally possible that internally they have worked the numbers and found Paladin survivability on par at T13 gear levels with current mechanics (although this begs the question, that if this is true, why haven't paladins been considered overwhelmingly OP up until 4.3 itemization?). Furthermore isn't it true that the current design of having to frequently reforge/regem around hitting CTC cap presents a very serious quality-of-life issue in the face of the intention to make epic gems difficult to obtain?