Thoughts about a mimeType equivalent to text/uri-list

Thanks for the well thought-out spec.
I know that for the MVP, the focus is on serving HTML via the text/html;profile=mcp-app mimeType.

And I know that you have left the spec open for extension later on ("other content types are reserved for future extensions").

MCP-UI supports: mimeType: 'text/uri-list' → Render in a sandboxed iframe using src

Do you envision that iframing a straight uri like this may ever be a post-MVP feature, or do you see technical or security reasons why that would never be advisable?

Btw, I did read the conversation here about the ability of a Host to pre-cache HTML-based resources, and that is a fairly good argument for why you've started with text/html:
https://github.com/modelcontextprotocol/ext-apps/issues/298

Thanks!