This is interesting, but like others I think HTML should be kept strictly for templating, and this adds an unnecessary amount of logic. It might be tempting to see this as removing complication, but in actuality it will probably add to it by reducing separation of concerns.

I think it would be good for less ambitious projects, but in the end it would cripple the building of more ambitious ones. If we already have Angular/React/Components/Whatever, shouldn't we just keep working on them and leave the HTML spec unpolluted?