Some Linux mint questions.

1. Depends on reliance on X11.
2. Maybe.
3. Probably not.

If you got enough experience to ask this, it might me a good idea to move to a KDE-friendly distro. AFAIK, Linux Mint does not like KDE.

Mint has been a very good conservative distro so I hope they continue in this fashion: transition when the rest of the ecosystem is already there so that there will be no pain for non technical users

Cinnamon is a super simple DE for simple people. I don't mean this as an insult, some people just never even think to customize their computer and are scared by settings and options. Just use KDE if it has features you like, you clearly sound like you're up for the change.

1. Years.
2. IDK
3. No.

Cinnamon development is glacial. It works, but the project simply does not have the resources to properly keep up or even triage important fixes.

It's one of the reasons I didn't stick with mint, and tend not recommend it if someone can use something else. When I stopped using it, the setting that was supposed to allow games in fullscreen to display without compositing was borked, costing you frames and latency. It had been that way for years.

1. They have an experimental Wayland session already. It mostly works except for some pretty important stuff...I also haven't seen development on it for a long while.
2. I think this is almost a 100% no.
3. I tried to implement that myself. Making them shorter than the screen is easy. Making them appear above the edge of the screen is hard, but not impossible - the code is in JavaScript and the logic is kind of disjoint across multiple files and stuff depends on panels being at the edge of the screen - I didn't do it in the end because it was too much effort for something I didn't want that much.

I expect Wayland cinnamon will be good enough to use by next years Ubuntu LTS. And the default in the next LTS after that.

Maybe.

Not to my knowledge