> What I am leaning towards now (although, I hope that more ideas can
> still surface in this thread), is simply re-using transient menu. Maybe
> with a couple of simple extensions (default action, menu UI, and the
> !arg macros we introduced).
>
> Then, we (or third-party packages) can implement code that will take
> transient menu definition and convert into what
> which-key/context-menu/eglot can understand.

Not a problem for context-menu-mode since it's possible
to write an adapter context-menu-from-transient like the
existing context-menu-toolbar thru context-menu-buffers.