This is a proposal to support MR frameworks/plasma-framework!500 (merged). The final target is implementing what is requested in https://bugs.kde.org/show_bug.cgi?id=332512.
With this patch kwin should make docked windows in wayland resizable, while preventing the user from tiling. MR frameworks/plasma-framework!500 (merged) would then be able to startSystemResize even when the docked window is frameless.
A demo of the final result: https://youtu.be/iSZcLh2yL1E.