I remember implementing the same thing in our framework like a decade ago, but eventually taking it out. We wanted to use it for caching data between tabs, so as not to hit the server again per tab:
https://github.com/Qbix/Platform/blob/main/platform/plugins/...
It had the concept of a “main frame” that they would route all requests to the server through.
I remember now — I did it not so much for tabs as for our solution of having tons of little iframes on a page: https://qbix.com/ecosystem
You can use a SharedWorker now instead of picking a tab to do that work (and failing over to another tab if it gets closed). Support is still spotty though.
Well, you can just use a service worker, instead of broadcast channels or shared workers. They have all the functionality you need, now.
Any iframe that loads in a secure context and itself creates a secure context, can load a service worker for its domain or subdomain or path.