It's actually not hard to carve out a subset of HTML you want, define a protocol you want to use over the existing implementation [0], then go back and implement that without the web at some later date if it's popular. If it isn't popular, well, it runs on the web. But doing things this way would indicate that you know what you want to get out of the redesign, which in a lot of cases, I don't think programmers do. They just know that the way it is isn't how they want it, or the thing they want to address is that the browser isn't quite the entire OS yet and it would be nice if it were just a little bit bigger.

[0] https://prog21.dadgum.com/66.html