I think the effort going into browsers is a double-edged sword. It's nice that we've got so much work going on, pushing new standards, etc. but it's also making browsers more bloated and making it less viable to bring out new browsers.

As more stuff gets done in Javascript, and Javascript gains more APIs, browsers like Lynx, Dillo, Netsurf, and umpteen yet-to-be-written ones are becoming less able to browse the Web. Likewise, the effort required to "upgrade" them would be massive.

I think a consolidation of features would alleviate the situation a little: have a small "foundation" of required tech, e.g. a subset of JS (or WebAssembly) with few primitives or APIs, and have the browser pull in polyfills for everything else, including interpreters for fuller, newer JS standards, etc. If a browser is graphical, it could provide a bitmap-blitting primitive, and use polyfills for CSS, fonts, layout, etc.

The Chromes and Firefoxes of the world could ignore the polyfills and keep going with their highly-tuned native implementations of these things, but it would prevent "kicking the ladder away" from everyone else.