OneNote isn't going away, it's just being removed out of the ProPlus/Office 365 installer and they are moving to a Windows 10 app version of OneNote. It's still very much in play and not going anywhere.
I still recommend OneNote for us inside of Teams. However, Wiki does work as well but it's a bit more for simple notes and what not, but you can have conversations around sections etc. But it does similar to OneNote and has very good load time performance vs OneNote, so it's a good place to stick channel notes / links / Dashboard for quick reference
I would recommend against a Wiki right now. A few months ago, they weren't searchable. Today, when you search for something and it is found in a Wiki, you get a link to a DocumentName.MHT file, and clicking on it downloads the MHT file rather than taking you to the wiki.
So progress is being made, but without search, a wiki isn't of much use right now.
I strongly agree with having the default notes app in Teams meetings being OneNote. OneNote is fantastic for taking notes (digitally or handwritten) and should in my opinion be the default - or at a minimum an option.
I'm a big fan of OneNote and the fact that it's being removed from Office Pro installation makes me really disappointed. I think this is a big loss for a lot of productivity gurus and OneNote lovers...(having the rich functionality of the desktop app that is...)