I just thought of something. Not that they're friends, but Adele and Dave Grohl seem to get along pretty well, based on the very few Grammy encounters they've been in. As mentioned by someone else before, it's important for her to get along with her collaborators, otherwise nothing comes out of it. Maybe she should enlist him for a few songs for her next album?
Adele and Bon Iver would be gold too.
Maybe enlist Brittany Howard too.
As mentioned by Maddox and Ichi, I agree, the nostalgic themes doesn't really translate well when you listen to the album from beginning to end, and I think it's because there isn't really a progression at all in the album. 21 sounds like there is a story arc, while 25 sounds like it lacks one. Imo, that's the main issue with the album. I hope for the next album there's some sort of story/progression.
Personally, I don't it's a problem if she keeps singing about love/heartbreak. For example, 1989 was different for TS, but most of the album is still about boys/love/break ups. Adele can keep writing love songs.
Edit: I'm betting that Adele will enlist at least one of the artists she shares on Twitter.
Edit 2: watch, nothing that I said will become true

she'll instead go full-blown pop.