The problem with the PGTK frontend is it is notoriously EXTREMELY slow. The latency on user input compared to the X11 (especially Lucid) version has some people reverting back to X11/Lucid.
When I do run Linux I run Wayland, I daily drive macOS, but better than both are what you already allude to: the Emacs widget toolkit which will focus on replacing the GUI frontend with SDL and also (equally potentially) introducing an actor-type framework (akin to BEAM's) for communication to decouple that GUI.
When I do run Linux I run Wayland, I daily drive macOS, but better than both are what you already allude to: the Emacs widget toolkit which will focus on replacing the GUI frontend with SDL and also (equally potentially) introducing an actor-type framework (akin to BEAM's) for communication to decouple that GUI.