I put some thoughts into this idea... and the more I think about it, the more I actually like it. Especially because I do not see a future for Gnome-Pie on Wayland. A clean rewrite as Gnome Shell extension might be a good alternative... Maybe I will come up with a prove-of-concept implementation in the next weeks! Thanks for this idea!
The performance will let a lot to say in my opinion, if this will be an extension of Gnome Shell. Also if it will be in that way it can block the compositor thread of Gnome Shell. This is the only thread that exist in Gnome Shell, where also is running the WM (Mutter).
Please note: In Gtk 3.0 you can merged a Clutter actor with a Gtk widget. Also in theory you can use an extension point and load the original widget that was wrote on Vala in gjs, but well this is in theory because of this issue: https://gitlab.gnome.org/GNOME/gjs/issues/109
It can be rendered also in a GPU if for example instead of Gtk 3.0 it will use Clutter or if it will use Gtk 4.0 when will be released (related to #151), but be an extension of Gnome Shell is different of use Clutter. Be an extension of Gnome Shell is what i think that will not be good for now. But is my opinion only...
I wanted to also chime in with my viewpoint on this. I use Gnome-Pie on KDE and I bet many other people use it on some non-Gnome wm (window managers) and de (desktop environments) as well. Though I don't think you have to officially support any wm or de other than Gnome.
Of course if your OpenPie framework works fine without Gnome then theoretically someone can make a non-Gnome version of it - better than nothing.