I like that last comment, btw, because if the criteria were just 51+ states this would be an easy NO.

As is, best candidates: Puerto Rico (Guam is a very distant second) on the territories-not-yet-states front. PR has a congress seat, even, though it's not a voting one. Other than the original revolutionary gang, every US state has been a territory before making it to statehood with the peculiar exception of the Lone Star Republic . . . and maybe Hawaii? I'd have to look up exactly how that went down, but I thought Hawaii was a territorial holding for a while.

Aha! But those of you paying attention note I've left one out - the curious case of West Virginia. Which suggests that there's a reasonably good chance that we gain another state by subdividing an existing one . . . probably California. There are some thoughts about parceling eastern Oregon out, but the planners there want "Greater Idaho" generally, so probably not gonna get a new state out of it.

In terms of most probable, I think it's probably PR joining as a full state, followed by Jefferson, and then a long tail of increasingly unlikely secessions and territories. But it's all still pretty unlikely - the current political landscape in the states is too polarized to allow for new state admissions to be anything but a bloodsport between the side that stands to gain new seats and the side that would rather burn the whole thing down that allow them to gain. Whichever those end up being.

Call it at most 5%, and only because you have such a long time horizon for weird stuff to happen.

@AndrewHartman Any reason you don't mention DC? It's at least in the running imo and if Dems ever get a trifecta w/ supermajorities they will probably do it.

@Kraalnaxx Trifecta with supermajorities is much less likely than another plebiscite in PR (for example). There's also a statutory objection to its statehood that came up the last time.