i feel like i know where you're coming from here, this isn't exactly what you're describing, but it's pretty dang close. really made the transition to window tiling far less intimidating than i imagined.

https://regolith-linux.org/

This was pretty close, but ultimately was too i3-ish for me. I'm also realizing that I could never be as productive with i3 as I am with a mouse or trackpoint -- with a trackpoint I never have to change my hands out of root typing position, whereas to hit any of the key combinations involving the super key, I have to move my left hand to a whole different, scrunched position. Don't know how you guys do it.

Thanks for mentioning Regolith and I'm pumped to hear that you find it useful!

I'm gonna try this it looks really good and exactly what I want.

You can add a nice bar to i3, and probably do even more customization. I'm guessing it wouldn't be to difficult to fork. It's a learning curve, but not too difficult to get over (I'd analogize it to vim). It's nice and easy to use, you just have to know how.

Have you tried Xephyr (nested X sessions)? Not sure how well it'd work with all of i3's keybinds, but perhaps worth a shot.

You could go the other way - i3 supports floating windows, so you could default to floating, or have default vary by program.

The issue isn't about whether you have floating available, it's about whether you have the batteries-included of a full DE. Bars, Settings, Networking, volume control etc. You can set all of these up with individual programs if you're a dogmatic adherent of the unix philosophy. But, it doesn't make for a very cohesive experience, and getting it all set up can be an enormous timesink. Different people have different levels of tolerance for that kind of incidental complexity.

There’s no reason you can’t run i3 window manager and Gnome apps.