The goals:

• a place where a more general public can be reached.
• to be able to make official communities. this has been very difficult to do in most instances (from personal experience), since many projects/people have policies that do not allow official communities in highly politicized instances.
• to be the entry site for the lemmyverse; facilitating the transition of novice users to subscribe to the communities of other distances according to their interests, leaving the political issues to those instances.
• focusing more on the user experience than on technical issues.
• generating a brand/identity of its own.

what does it mean community of communities?

Basically it’s a parody/joke about the Metaverse.