I'm just nitpicking that it isn't, in fact, common.
Well im glad you dont think its a bad idea. But i will point out, whether you think this system is common or not, most of the games that have it, are in fact in the top 10 rated mmo's. Unlike the list you provided.
2 of which are games cryptic has already made. Therefore, it shouldnt be that hard for them to do it again.