"I would go so far as to argue for deployment of a self-contained webservice to the end users that could be accessed via any arbitrary localhost browser"
Might as well use Unity game engine and write your app inside one.
There seems to be some people writing UI applications with the Godot game engine. Given the dismal state of desktop UI frameworks/tools, this seem to make more and more sense (very light binaries, solid cross-platform support, a WYSIWYG toolkit with good scripting functionality, a high-performance 2D renderer, access to C/C++ if you wan to go low-level, you name it.)
Well, the two applications I’ve linked above are very graphically intensive (the first one is a map designer, and the second is an image editor), up to the point that it will be meaningless to add any screen reader or dictation support. In some cases you’ve got to admit that it’s close to impossible to bring certain features to people with certain disabilities (although I think this should be its own field of HCI research, maybe it can be possible someday?)
Might as well use Unity game engine and write your app inside one.