We could have amazing HTML/CSS performance if we had programmable "HTML to bitmap" caching. But: a) it's not secure if we can render HTML to bitmap and send over network, b) cache invalidation problem - we'd have to invent mechanisms to lock HTML against further changes or track changes and rerun "HTML to bitmap" procedure.

All this is not suitable for web, but for thing like Elector - hell yeah. HTML to bitmap extension would be really welcome. Then you could render UI in WebGL or WebGPU. Adobe Flash had something similar if I recall correctly.