Small thoughts of mine this afternoon.

HREF on any element
One of the planned changes for XHTML 2 was to allows href to be an attribute for any element, not just <a>. It's not that huge a change, indeed backwards compatibility could be forced using javascript. Since it doesn't face the same technical challenges as other HTML 5 adjustments I wonder why it didn't make it into HTML 5.

Where's my default inline block container?
<div> is display: block by default. <span> is display: inline by default. Where's the default inline-block element? Also, I feel each major display type should have a corresponding element. <grid> for display: grid, <flex> for display: flex and so on. As for inline block - I'd vote for <IB> as its default container.

Canary Mode
Browsers will try to render anything. What if they didn't? I'd love it if I could get Chrome or Firefox to cease rendering on an error when testing my own pages. Never would be able to turn it on to browse the net at large because most pages have invalid markup, but it would be nice if browsers would at least help you learn standards instead of helpfully rendering everything thrown at them.