Rather than monitoring anything, why not have a system where users, after having completed the RPs required, post in a level-up app thread?
For example... Someone comes up with leveling rules. Ex.: "Completed RP" = RP with 2 pages per character involved, and whose interactions have come to a close (maybe the thread gets closed, or maybe the user just posts "--end--" in their last post).
So for 2 characters in the RP: 2*2=4, so the RP needs to be at least 4 -whole- pages long.
For levels 1-10, 1 completed RP is +2 levels.
For levels 11-30, 1 completed RP is +1 level.
For levels 31-50