My guess is that PvP will make more sense at the level 95 cap, when the trait tree was introduced, and the code hasn't changed drastically on PvP since then. They did a lot of re-tooling around the level 95 level and 100 level to re-balance PvP (there were a lot of complaints back then) and those code changes is essentially - give or take a few minor ones - the code that current level 120 pvp runs on.
Wasn't there some stat-wise change from 105 to 106 (Mordor ->)?
I tried with my hunter back then with the golden gear and stuff from North-Ithilien. Stats were ok'ish at most, but leveled up to 115 shortly after to be (more) competitive.
I have no guess WHEN it could be happen, if they plan to stick to the "normal" scaling system. And what shall we do when Rohan kicks in? I am afraid servers will be empty after 75 without Moors :-(