I think Songs of Ascent will happen and I don't think this will be their last album. I do think a bit of a break will take place after the E&I tour, since they've been a bit active. Adam just had a kid too. While I did enjoy JT2017 generally, I would've preferred them not wasting time to tour a 30 year old album and either wrote new music or wait to have just toured SOE, but I guess Live Nation touring commitments got in the way and there's too much money to pass up there.
I love Achtung Baby with all my heart and it's one of favorite albums ever, but I sincerely hope they don't do a Zoo TV redux tour in 2021. That era is special and significant for good reason, ahead of its time and a a band at the peak of its powers, just let that live on. I am jealous of all those who got to experience it first hand, but I can tell even from just reading about it or watching footage from that era that it was special and a game changer.
I don't necessarily mind them playing more AB songs (rare ones too) during the next tour, assuming they have an album ready to go in 2021 and they can maybe do some homage or what not, similar to the Vertigo Tour/Zoo TV style encore. Of course, U2 is a business, so the money there would be too hard to pass up, but we'll see.
Overall, I think a few more albums are in them, though it's both a blessing and a curse that they love to play live. Since every tour needs to be a giant spectacle and they have to tour every release, it might be tougher to put out more music. I'd prefer more music at this stage and surely they can tour, perhaps just less, which might be the case, but who knows?
I'd love to see them make more music into the next decade though and I think they will, plus hopefully when they call it quits, the U2 vault will be open. From the Rick Rubin sessions, to the RedOne stuff, to all that Passengers material, I mean, my goodness. Perhaps something similar to what Neil Young is doing with his online archive? I would certainly be very happy.