What will be the 51st state? DC? Puerto Rico? A handful of conservative counties in Colorado? A wildcard?I continue to think that the failure of the Democrats to push DC statehood in 2009 (and, for that matter, 1993) was odd, at best, and inexplicably foolish, at worst. The District certainly has the best case for statehood (and, yes, there's also a legitimate case for just returning it to Maryland). But Democrats seem mostly uninterested in pushing something which most of them agree with on the merits, not to mention something which would get them two safe Senate seats.
As far as I can tell, nothing else is close. So I'll say that the most likely possibility is that Tea Party Republicans win Congress and the presidency and chop up a reliably Republican state to make two reliably Republican states. Utah, maybe? The Colorado plan doesn't work as well; it would presumably create two safe Republican Senate seats, but make the rest of the state, which is now a lean-Democratic state, into a safe one for Democrats. But maybe they would do that one, too.
Really -- I don't expect much of anything any time soon. But those are the two most likely, with anything else requiring significant changes in the parties or something more dramatic (I don't know...what if Florida becomes an island from the oceans rising; could island Florida want to split from mainland Florida? Or would it just be like Michigan and the UP, or New York and Long Island?).