You know, I had a look once back when I was a DM at adjusting the tables to modify the experience curve.
It's a 2da file that with various amounts of experience points from any given level monster at any level range the PC might be, further modified by a multiplier based on how many levels are between you and the monster.
Tweaking the exp table would require is to sit down and look at the CR of
every monster you might encounter in a given area, consider the range of levels of the PCs that might fight it (accounting for every build possible--okay, that's not actually feasible, but accounting for the widest range humanly possible), and then ALSO factor in the experience curve based on the average party size.
When you're done with all that, you go back to your table and....start randomly incrementing the values up and down. Then, you go back in game to test if the area feels right with the new balance and HOPE your changes were "just right." If not, you go back to step 1, and you tweak the value just slightly once more. Then you save it, load up your server, test, tweak. Save it, load up your server, test, tweak.
Then when you finally get it all done, and you've achieved the perfect balance for every area range and every combination of players with every combination of items...a year later new spells, feats, vendors, classes, and such are brought in and the balance completely changes once more.
I suggested then that we shouldn't try to urge the developers to implement any changes ot the exp curves in the game because it was such a huge headache to tweak. It's just too much time, effort, and energy spent for a result that might end up no better (or maybe even worse) than the original vanilla curve that we use.
That being said, something like "RP exp" could be introduced for when you kill monsters for a prolonged period of time.. but it would be pretty silly to get exp on top of exp. There might be other ways we can adjust the leveling over time, but it'd have to be in small ways over a longer course of time.
I personally had an idea for a system that allows you to put placeables on the map that trigger dice rolls vs various Lore skills and award you with a bit of exp and a small blurb of flavor text about the area you're hunting in that you can RP about. Like a Knowledge: Nature check in the woods that identifies the specific types of trees and local fauna, that sort of thing.
Still, anything is a long way off, for now.