I'll choose to be optimistic here and note that politics are never static and coalitions are always changing. We seem to have been in a stasis in terms of trends for the past 10+ years with Obama -> Trump eras, but there is obviously a constant incentive on both sides to win elections and demographics will continue to shift.
Off of this list I could see AK, UT, KS, TX, and MT (yes, I know Tester is there now and will likely lose) as long term pick-ups. Younger, less (evangelical) religious, and/or higher 4-year degree levels. Throw in NC and those are 12 potential pick-ups in the next 5-10 years to offset slipping in other areas. In short, I agree it may be 3-4 cycles but don't expect two decades for the Dems to be in contention for the Senate
UT? Seriously? There's not even a functioning Dem party in Utah. They've been nominating Republicans (e.g. Evan McMullin) to run for Senate.
AK will never go red because of its absolute reliance on fossil fuels. Well, won't go red as long as the Pubs' energy policy is drill drill drill
TX? Maybe. I'll believe it when I see it, but it's not impossible to imagine. But the Dems have to clean up messaging with Latinos. And I don't see the time frame there as 5-10 years. Maybe 10-15. In 2018, in a red wave election, with the best Dem candidate in a while (Beto) going up against the most reviled Pub candidate (Cruz), Cruz won and it wasn't really close. Close by TX standards but 2.5 points isn't really close for an election and again, that was the best shot we've had in a long time. I'll happily eat crow if I'm wrong, and the Dems absolutely should be spending money in TX (you can't win a state if you don't invest there), but it's still entirely speculative.
I can't speak to KS. I have my doubts. The Republican Senators from that state most recently won their elections 60-39 and 55-41, so there's a LOT of work there. Don't be fooled by the gubernatorial election. MA has had Republican governors. MD had one. CA had one not that long ago (Governator).
That leaves us with NC. Absolutely 100% the best pickup opportunity along with the Senate seat the Dems will win when Susan Collins retires. And RonJon's seat in WI (though that's going to be a tough one).
***
On the flip side, we're currently holding many seats that are tenuous. If you look at the current swing states, Dems improbably control almost all of the Senate seats there. 2 in AZ, 2 in NV, 5 of 6 in the Blue Wall, and 2 in GA against 2 in NC and RonJon. That's 11-3. If those states remain tossups, it seems unlikely that the Dems can continue to hold all those seats. The GOP definitely has suffered from own goals in those states. They probably aren't going to nominate Herschel Walker again, and since Warnock could barely beat him, I have my doubts about Warnock's longevity (though he will have more incumbency going forward). I don't know if the GOP can find decent candidates in AZ, but I would not assume that we will be running against Blake Masters and Kelly Lake for all eternity.
And of course, WV is gone and it looks like MT is as well.
Obviously if the country shifts left (or pro-Dem, which isn't the same thing), this all can change. But if you assume that we're stuck with this electorate for a while, it's looking grim for the Dem hopes in the Senate. Which is why it was criminal not to make DC a state -- even if you disagree with my more radical plan to use DC as a constitutional convention.