Ouch! I had never thought of that.If X11 gets replaced with *shudder* Wayland, a lot of great software will be killed. For example the ubiquitous XTerm, SDL 1.2, Gtk+ 2.x and other libraries that are quite critical for older software to work.
I would say wrong tool for the job.If you mean online websites provide services run on a browser, this is not what I want to mention.
I said about desktop app build using web technology, html5, nodejs, css... Ex: Atom, VSCode...
I dislike web techs with a passion (but html and css), they ruined internet for me. By using them for GUI, you are just turning the GUI experience into the same misery that it is using modern websites.