Today integrations, custom components and the like are relatively tightly couple to the core; they’re written in python, import modules, expose functionality.
If there was a message bus that could be accessed by external programs (obviously with well define message types and data structures) then it becomes possible for totally independent programs to be run, connect to the bus and provide functionality. These programs (“agents”?) could be written in different languages, potentially even run on different machines (if the bus was network exposed) and would be loosely coupled (restarting the core wouldn’t require an agent restart, for example).
To a small extent this is currently possible via MQTT but there’s limited functionality exposed this way.