The deeper I got, the more I realized really supporting the entire LaTeX toolchain in WASM would mean simulating an entire linux distribution :( We wanted to support Beamer, LuaLaTeX, mobile (wasn't working with WASM because of resource limits), etc.
I'm not against typst. I think it's integration would be a lot easier and more straightforward I just don't know if it's really that popular yet in academia.
The WASM constraints make sense given the resource limits, especially for mobile. If you are moving that compute server-side though I am curious about the unit economics. LaTeX pipelines are surprisingly heavy and I wonder how you manage the margins on that infrastructure at scale.
You are right in pointing out that the Web browser isn't the most suitable UI paradigm for highly interactive applications like a scientific typesetting system/text editor.
I have occasionally lost a paragraph just by accidental marking a few lines and pressing [Backspace].
But at the moment, there is no better option than Overleaf, and while I encourage you to write what you propose if you can, Overleaf will be the bar that any such system needs to be compared against.