When I built this I specifically didn't want to have to provide feedback and then submit it back, then open again after the agent had considered my feedback.
The way discuss is setup, it's interacting forwards and backwards on the discussion, from the web page, but within the original agent session I was having.
Very convenient to ask a question "in the document" and get a response a few seconds later, in the same document.
No reason MCP support couldn't be added.