I like it. Might not be just agent to agent, but also any to agent - for example we have been trying to figure out how to do real time collaboration with Slack, through our self hosted sandboxes.
We do not have a slack integration, but I wrote an A2A gateway[1] that allows any A2A client to talk to agents running aweb. The code would share a lot. Do get in touch if you want any help integrating this, I am juan at my site.