I don't know if this has been mentioned yet but someone (I don't remember who) found a correlation between IQ and maximum possible rating (if the player worked as much as possible to improve). The guy found the formula to be:
Max Rating = 1000 + 10*IQ
Since the average person has an IQ of 100, an average person could reach 2000 (according to his study).
Actually i think having a FIDE rating of 2399 up to whatever you have very good chance to make a living; everything will depend on your success in tournaments.