As a man with a perfectly unhealthy obsession with pirates, I'd love to see a Pirates of the Caribbean line based off the new film coming out, with minifigs in flesh colors so that I can spend twice as much on my MOCs, fretting over whether I want to stick to good ol' yeller or make it more realistic. LEGO, my how you tease me....
Another great line with a well-developed mythology and plenty of fans would be LOST. Especially with all the glimpses into the island's past, I could see it being a virtual motherload for MOC opportunities and custom minifigs. I assume the smoke monster would be just a giant conglomeration of black ice cream pieces.
Actually, it would be really nice if LEGO could make short sleeves for minifigs. Like an arm that is half one color and half yellow/flesh. It's hard to make believable hot weather MOCs when all the minifigs are either in long-sleeves or wifebeaters.
As maybe one of those individually packaged minifig series that are debuting in June, I'd LOVE to see a best of the best historical figures line from politics, science, and entertainment. Abe Lincoln, Einstein, Charlie Chaplin, etc. Of course, this technically wouldn't be a license so unread everything I just wrote.