Now's your chance, Google Plus!
Alas it didn't work out.
It's hard to remember how good it was, I remember it being better than Slack, Teams and Discord are now. But maybe that's a false memory.
The simultaneous editing became integrated into Google Docs than in MS Office but I feel like neither really reproduced the magic of Wave. IMO the key ingredient was the chat format: you could go directly from messaging to co-authoring without having to like setup a google doc or send a sharepoint link etc. and then you could keep messaging in the same window.
I guess Notion is the modern equivalent? I've gotten burned on hosted notes products too much at this point though.
Protocols like ActivityPub do not come even close.