Reminds me of when Aeris Irides tried to connect (streams) (2021's umpteenth fork-of-a-fork of 2010's Friendica, to dumb it down) and OpenSimulator (free, open-source server application for 3-D virtual worlds very similar to Second Life, est. 2007, interconnected 2008).

Okay, this wasn't to go as far as federating the OpenSim local chat or even only the OpenSim in-world instant messaging system via ActivityPub because both (streams) and OpenSim were to remain untouched. So you couldn't post from OpenSim to Mastodon or vice versa.

But the planned features included

tying together the creation of channels on (streams) and the creation of avatars in OpenSim
forwarding notifications from (streams) to OpenSim as a message
syncing the avatar profile picture in OpenSim with that on (streams) bidirectionally
automatically uploading snapshots taken in OpenSim to the (streams) file space and generating image-only posts

Nothing came out of this, though. The HoloNeon (streams) instance is gone the HoloNeon grid is gone, and Aeris has moved to another OpenSim grid.

So neither the idea of interweaving the Metaverse with the Fediverse is new, nor is the free, open, decentralised Metaverse.