I don't know what the exact number is off the top of my head, but one of the aspects of the system is that newPvP gear, regardless of what "tier" it is, will hit cap expertise. That is, getting higher level PvP gear won't increase your expertise stat, just more of every other stat.
Rob, can you comment on what the new total maximum expertise achievable will be?
Currently it's what, 1395?
With the changes you're mentioning and the removal of diminishing returns, this implies all PvP players will want to max expertise on every gear set.