This makes me wonder if you could define a subset of those standards that would support 90%+ of the use cases, would be simple and efficient to implement and would be supported by existing browsers. You could then push this light version of the web as a new base for a future standard.
The problem would of course be that you would have to keep around a different browser to render old sites. Could still be worth thinking about. Doesn't seem feasible as a long term strategy to have browsers support thousands of apis and increasing.