I have already tried to imagine acronyms of my own – the ones that actually mean something of course.

I was thinking of a metaverse which would have several character names under one login name, so login name shouldn't be told to anyone. The login name could be a second password to access all those alts. They would share the inventory, wallet and inbox, though some items would be bound to a character. One character is free, more will cost.
It falls in the line with IMVU and Second Life, with an up to date graphics and engine. It would also have a MMO region that can actually be played like a game, but with a unified leveling and combat system (with PvP). It could also be a way to win free currency. All the rest of the areas would be just for socializing, building homes, recreational areas, clubs, etc.
There wouldn't be secluded public rooms, rather secluded free roaming realms with their own grid systems and communities. Maybe it could be a tree hierarchy. The further you go in a branch the more specific interest that is.
I wouldn't mind enabling walking in the free roaming concept. When in IMVU, do as IMVUers do... but to face the reality, most players usually expect walking in every game with controllable humanoid avatars for it being a basic, natural action. For IMVU, it's just too late to apply it. If there's walking, it should be there from the start.
The groups features would be incorporated into the client, including group chat, forums and calendar with a link and countdown. Some areas would only be accessed by a group. They would have a visible role in the social actions.
ABC music system with various instruments also exists but it's not very widespread within games. It's still very popular where it is and never fails to bring people together (case in point). It allows users to compose, and so it could make a great addition to a virtual catalog. Maybe call it "sheet music". One band member creates or buys it and and he's able to share it with his entire band. I think it would have less copyright issues at least, since all such music would be considered as cover arrangements or originals. There could be competitions and marching bands.
Perhaps the ABC files could have some timed lyrics in the comments, and the singer would be allowed to have the mic.
Sure all of it would be ambitious to say the least, but I know that all of this has sort of been done already. But bringing all this together in one world would be highly addictive. So far I have only played with such an idea.
But bring your ideas of a "perfect" virtual world and see where we can agree. Not that we have to actually do it after brainstorming, but wow, if a new virtual world gem arises from this place, would that be a story!