Well its not one T4 zone is it? It’s multiple T4 zones. Like all the lvl 70s in WoW aren’t all in one place. There are multiple T4 RvR zones. Plus scenarios, instances and PQ everyone not going to be in the same battle.
WoW going to get a massive outdoor RvR area in WolTK. Not heard of any limit on player numbers.
There is a front line in each of the 3 T4 zones... so if you have 50% of your 3000 at the 40 rank cap, you'll have 250 per faction side in each of the 3 zones. 50% of the rest of server is in scenarios, instances....etc
The whole point if it all though is to sack a city, and do to so, you'll be on the front line in one of the three T4 zones, playing a game of tug of war. If you are RvR there is no point being in an area of the T4 zones that are locked, you'll be on the front line.
As far as wow goes, it'll still be the same 'omg I cant control my character, because I have been feared, stun locked, mind controlled, scatter shotted, noob coiled, scared,' and everyone playing for themselves rubbish that exists there already. Add into the mix that skill nearly counts for crap because it is all based on your equipment and a cookie cutter talent spec.
I am only rank 22 in War, and I can tell you that the RvR is light years ahead compared to wow and i've done wow pvp for 2-3 years (stormscale). Another point to make about wow, every night there are at least 200-300 queues on Stormscale, so it is capped is it not?
Edit: Oh, and Stormscale not being a carebare server I can tell you that there is sod all PvP going on in the zones that have objectives. Very rarely do you have any sort of mass PvP mayhem taking over these zone 'objectives'. Probably because they dont really provide that much for the zone/game. World PvP is dead if World Of Warcraft (should be called World Of Battleground Instances), unless you count the gankers. End of.