Alaska is definitely trending Democratic. I'm not saying it'll be voting like Washington and Oregon anytime soon, but the potential is there and little cracks have been appearing in the Republican machine for years now. Stevens losing in 2008 was a canary in the coal mine for the state GOP, suprising me even after his conviction.
Utah is rockribbed Republican. 2016 proved the Republican fidelity of most interior western Mormons. Hillary Clinton, Evan McMullin, and Gary Johnson all thought they had a legitimate shot at Utah's electoral votes, and look what happened. I could see a blatantly anti-Mormon Republican nominee putting the state in danger, but as the years go on I think there's less chance of such a GOP nominee.
Idaho will be one of the last four or five states in the nation to go Democratic. It would take a special combination of a truly national landslide, mass Mormon defections in the southeast, etc. Very, very unlikely but not "impossible."
Wyoming would be the last state to vote Democratic. This would be one of the states to vote Trump if he gunned someone down on Fifth Avenue. The Democratic brand is, has been, and forever will be toxic in this state. It's cowboy country with coal mines. It's unwinnable. I won't see it flip if I live to be a hundred.
North Dakota for the foreseeable future may be unwinnable, but what happens if/when the fracking boom goes bust and all those oil field workers leave the state and Williston turns into Butte-on-the-Plains? This is long-term stuff but people need to remember that North Dakota is historically highly elastic. In 1920, 1940, 1952, 1980, 2000, and 2016 voters reacted violently to incumbent Democrats. Then they turn on the GOP, massive swings to Democrats/third parties happen, and people talk about "it's a swing state now." All that being said, ND is unlikely in the near future, but not unrealistic in the long run.
South Dakota doesn't have extractive industry on the same scale as its northern twin but is also highly prone to violent anti-incumbent swings and general weirdness. That being said, it's voted Democratic only four times in history (1896, 1932, 1936, 1964). Unlikely in the near future, but not impossible forever.
Nebraska: I'm waiting for the Lincoln-based district to flip, at least once, in the near future. Probably in the next national Democratic landslide. NE-2 will tag along of course. NE-3 last voted Democratic in 1936 and I'm actually confident predicting it will never vote for another Democrat before its inevitable demise. Nebraska at-large is unlikely in the near future, but somewhat more likely than, say, Idaho. The problem is, even if NE-1 goes narrowly Dem and NE-2 goes solid Dem, the Republican margin in NE-3 will be very tough to overcome.
Kansas: I think the 2014 races were a red flag to Republicans, or should have been, and Clinton nearly winning Johnson County even more so. This is one state that has been so screwed up, frankly, by radical right-wing experimentation that I expect it to vote for the next landslide Democrat as a "screw you!" to those people (and then return quietly to GOP supremacy as it always does).
Oklahoma is unwinnable for the next few generations, if not forever. If Wyoming is the last state to vote Republican, Oklahoma is right there with it. The culture, demographics, etc are just brutal for Democrats.
