Why PvP arena is made available beginning at level 30, but PvP provides no amount of EXP (I am talking about regular EXP, not PvP EXP. The EXP that levels a character from 1 to 50) to level a character past level 30?

I interpret this decision to mean that SE envisioned PvP being an End Game event. Why would a player whos highest class/job is 30 participate in PvP if character progress in the rest of the game stops during PvP?

SOME amount of exp should be awarded to PvP participants. Perhaps, give winning teams a little bit more exp than losing teams. However you all end up deciding to do it, give players under level 50 EXP for participating in PvP.

Does SE have any plans to award EXP to PvP participants? If so, when will this change be implemented?