Claude Code’s been doing this for at least a year already and I assume Claude Cowork does it too as a result. That’s already millions of users, so it’s not “just a neat idea with no adoption”.

Also it's not that hard at crawl time to transform HTML into markdown before passing to the LLM.

I mean, it's exceptionally easy for them to add it. Even with low adoption. Somewhere in the bowels of chatgpt there is code that queries for html, and then parses that to markdown or something similar. All this would be is adding the logic to request markdown if available, then bypass the html->markdown step if you get markdown back.