Tempus Kittredge, the knight of legend that really want to unclan.
Under the current system somebody can still throw their weight around and act like a jerk when they reach the xp to unclan, feeling invulnerable, but at least it limits how often they can do it. Also, it would provide more opportunities for cross-play if people can just clan each character, level to 50 and then discard it- not that you would do either of the above of course, but I'm sure there are some who would.
I do think an alternative would be to have some requirement based on the number of hours you have played a character, rather than just on xp. Or perhaps two options, one based on xp, the other on hours played- but I don't know how feasible that is.