[bobthepanda]

What would you suggest, that is compatible with its goal of being a markup language?

A lot of the machines built on top of HTML (e.g. JSX) add non-markup to HTML so you can handle if-else/filter and loop. But I don't think there's ever been interest in expressing that natively in HTML itself.

[jakelazaroff]

Some sort of native transclusion other than <iframe> would be really nice.

[kitsunesoba]

The main thing that feels like it could use work is the lack of adequately capable primitives/widgets. Many are plain missing while others are too basic/limited.

[asddubs]

native support for a form element to allow changing the order of a list using drag and drop.