"Something" like, sure. Tho note that depends on the $599 price point being more or less permenant at this point, and given the rapid price fall of 7800GTX without an Ultra to replace it at that price, I consider that an open question still at this point.
History would also suggest at least two R580, for yield purposes, so if they can hang on to that $599 price point, R520 still doesn't start until the $399 price point, with an XL at $299, and then midrange around $250.
Tho, if they go that route, probably what I'd expect to see is R520XT retired after a short life, and R520XL as the "hanger on" from that generation, much like they sort of got started in that direction with X800XL. Yields/availability/margins/pricing would drive that kind of thing.