I think it would be great to have the possibility to use Budgie as a Tiling Window Manager. There are so many people who just like TWMs for how they work, and don’t want to lose their time configuring it along with xorg, the statusbar, notification daemon, app menu, etc. They just want it out of the box, like any other DE.
I’m not a developer, but I think it wouldn’t be very complicated to integrate i3 into an alternative Budgie session, since there is already a i3-gnome session and it doesn’t have much code in it: https://github.com/i3-gnome/i3-gnome
Curious if you noticed / tried Shuffler with the latest updates from daily extras ppa, a.o. this one: https://www.youtube.com/watch?v=j6mrrVpE5A0.
Shuffler is intensively worked on, with extended functionality with (auto) tiling to sections of the screen etc. for 20.10 and later.
Note however that Shufflers aims on “hybrid” functionality and will not replace window manager’s way of working.
From looking into this in the past, there is no elegant way to replace the Window Manager in Budgie. And from various posts I have seem around, upstream has no interest in that work.
Options today are to either use shuffler as @vlijm suggested. Or you can install I3 on top and select i3 in the lightdm login window, but it will fall on you to configure I3 to use the various gnome settings daemon, etc