On Linux, we've just released our support for X11, removing the need for GTK. As we're drawing the whole app surface, we're always interested in adjust the UX of our controls on individual platforms. If you have examples, let us know.
Finally, for WebAssembly, our current rendering backend is using the HTML DOM, which means that accessibility and other native behaviors are functional. Same here, if anything accessibility related is missing, we're all ears!