I think it's a good idea to explore how an agent-isolated model can be used to simplify expressing "ownership" of the UI. It certainly seems worth exploring in some depth.

Another interesting angle is to look at how Maestro contracts can be used to express correct ordering of UI events, to control enabling/disabling of UI elements and force some formalism on UI interactions. Don't know whether that's actually going to prove useful, but it seems interesting to explore.