> turning web browsers into operating systems won't break the current monopolies, because it's the same companies in either case
False. Linux is a perfectly great mainstream desktop option thanks largely to web apps (+Electron). Basically everything's available. How incredible is that? Or swap Linux with any other alternative.
The fact is you can make an indie engine right now. It won't support most of the web, but then again you don't want any of that to exist because of the additional barriers to entry for engines. So what's the problem? Make it.
In your world, somehow every platform vendor stops making web browsers, and we might have a bunch of browsers with 0.1% marketshare. How? Ludicrous. And proprietary browser plugins, really? So you're not looking to reduce complexity after all, then?
Again I don't think you've thought it through.