We’ve had variations of “JSON describes the screen, clients render it” for years; the hard parts weren’t the wire format, they were versioning components, debugging state when something breaks on a specific client, and not painting yourself into a corner with a too-clever layout DSL.

The genuinely interesting bit here is the security boundary: agents can only speak in terms of a vetted component catalog, and the client owns execution. If you get that right, you can swap the agent for a rules engine or a human operator and keep the same protocol. My guess is the spec that wins won’t be the one with the coolest demos, but the one boring enough that a product team can live with it for 5-10 years.