I'd like to suggest a change in how you do experience points and player levels. Now that Empyrea is out, there are new potential player levels that can be reached. I believe Lvl 124 is the new max. That's great, but I reached Lvl 120 while I was halfway through Mirage, so any experience I earned while completing it was lost, which I think shouldn't happen. Experience points should continue to build up, even if I have maxed out on the available levels. Then when a new world becomes available, those experience points can be applied to the new potential levels. I'd like to see this be seriously considered.
The reason why the experience bar is removed after maxed out is because as you said, with the introduction of the new world; having all the gathered experience accumulating just to be given to you when the level cap increases seems a little pointless.
If that's the case, what's the point of giving experience in quests from future worlds? Don't you think that system would be abused by players?
I also feel that your idea may just cause major unbalance to the game KI is trying to cease in happening. We already have the critical/block system that's unbalanced. We don't need any more additional problems.
I understand what you're saying, but in the long run, it wouldn't be feasible.
An idea however if you're so concerned about XP, is to stop questing when you get to max then return when the level cap increases. That's what I do in some situations.
It hasn't been an issue while I was ramping up to Lvl 120, I don't see how it would be an issue now. While I was playing, several new worlds were added and I was able to play through all of them, building up levels without it unbalancing the worlds, I don't see the issue now with allowing experience to continue to be built after topping out on the available levels.