It's not just Zed, Emacs has has a thriving ACP implementation in agent-shell[0], and allows for some very cool integrations[1]. There are a fair number of other clients[2] as well.

[0]: https://github.com/xenodium/agent-shell

[1]: https://www.youtube.com/watch?v=HJQ86HuSIJI

[2]: https://agentclientprotocol.com/get-started/clients

The second half of this is spot on. The now is making IDEs that can integrate with agents, not the other way around. Soon the Claude and Codex will do that for us on their hosts and the argument is it will save sending the context up.