I know where you're going with Exiles, but let's examine the originals... first we have Blink, who by far was NOT a newcomer, but like I want a rather "obscure" character with very little previous history. We have Morph, who in spite of his alternate origin, was exactly the same as AOA Morph. We have Nocturne, who debuted on X-Men Millenial Visions. And we had a Cyclopish version of Mimic... The characters were nowhere new or unheard of. And the premise is "Alternate Realities", not necesarily alternate realities we haven't seen

I for one would love to see the alternate reality from What if 79 a bit more, or maybe the one in What if 12. Sure, create new worlds, but every once in a while drop in a what if world that was already created.