I think the Superman comics did experiment with making Lois african american in the 80's but switched back (Clark Kent was going into television for a while there, too).
And by the way, there was a Kenneth Branagh Shakespeare movie that had an african american cast in a major role (can't remember the name, but someone pretty famous), with Keanu Reeves as his evil brother! (I think it was "Much Ado About Nothing"). It seemed to work.
Once people get over the initial shock value, then it becomes no big deal.