I am a pretty big proponent of MCP, and I think this at least for now is not a move in a good direction.
The whole surface of the MCP specification is already pretty big, and barely any server implements anything beyond the core parts.
With elicitation there was already a lightweight version of this in place in the standard, and I'm not sure I've ever encountered a server or client implementation of it in the wild, and elicitation is an order of magnitude simpler to integrate on a conceptional level.
I fear that this has a significant risk of splintering the MCP ecosystem further (it's already pretty strained due to the transport protocol iterations), and there isn't really a reason to create a official extension (yet), that may worst case also require multiple iterations to get things right.