And Goodman Games has already done a bunch of the B/X adventures (B1+2, B4, X1, X2).Even as a fan of Mystara (I started there in the Basic days) I'm hard-pressed to come up with enough to justify it with Forgotten Realms, Exandria and Greyhawk all filling the kitchen sink niche. I think the best we'd see is some anthology of B/X adventures using Karameikos as a backdrop.