It's deeply rude to the user to strip away all the user agency they have on the web. The web is one of the only places in computing where users get more than pixels being pushed at their faces: walking backwards into the dark & shadow is a bad move.
Basically all the same faults and troubles of Towards a Modern Web Stack apply. https://news.ycombinator.com/item?id=34612696
It's also notable that your software is grossly immoral if it does not have accessibility. You could write your desktop app that renders into an HTML5 canvas to also expose a second render of the app that is the accessibility tree (or less kindly use some of the new APIs to grammatically create accessibility, but this is far worse an option). But this greatly increases the effort of the work, and it's effort you don't need to spend if you use actual HTML with semantic tags and some ARIA sprinkled in.