First things first, I found out the other day that someone actually built the major part of my vision: Constraints Oriented stylesheets (using cassowary).
This is how iOS now handles layout. It makes easy things easy, and hard things achievable. Exactly what you'd want.
Beyond this, I think that html has too many tags. To put another way, the browser should not generally permit <script> and <style> to exist in the same context that <em> can exist. onblah= attributes were a terrible mistake that we'll never be able to undo. It would be cool if there was something like a <content> tag which, within it, only permits content oriented mark up, while disabling scripting and styling tags. Likewise, forms, scripting, meta tags and linkages should be in isolated contexts.
And finally, what idiot decided that & ampersands should have a prominent position in many URLS and then use & for entity encoding in html, a completely different purpose. URLS now have to be http://entity&encoded
uhg. so stupid. what would be wrong with <amp> or <amp/> instead? or since we've freed up & for normal expected use, <gt> <lt> and <quot>
ah well.