Basically it is really hard to collaborate on scratch at the moment, what with either remixing loads or sharing an account and my idea was where you can create a new project/studio you can also make a collaborative project, similar to a studio you would get invited and could choose to curate or not. Anyone would be able to see the members and the leader(s) of the collaboration.
How it would work is that in the project they would all have access to is several people would be able to access it from their stuff and maybe even have a new tab on the side where unshared projects are and trash are called ‘Collaborations’ and in the project they would be able to see if someone was moving a block if they were on the same sprite. The only problem I could see with this is if a tug of war occurred. XD
The leader is the one who would be able to invite and remove people, delete the collaboration, promote others to leader and access the project. They would also be able be able to delete comments on the shared projects. The members would only be able to access the project.
Once the project is shared, I'm not sure yet if it would either show up under all the collaborations's people's projects or just in a new section on their profiles called collaborations.
If you have read this far well done and thanks for reading! My fingers are on fire!

Fully support!

This has been suggested like 500 times…

And as always, I say that it could be abused as a private chatroom.

Aside from that, there would be tons of server load. To transmit what each user was doing would require a server transmitting the data, and if it worked anything like cloud variables, than it wouldn't even work very well…