Pair Programming in MIT App Inventor

I teach PLTW content and the first about half of the class uses MIT App Inventor as a platform to teach students how to code. I'm assuming that PLTW and MIT App Inventor have a working relationship, otherwise that probably wouldn't really be possible. That said, I'm rather frustrated that there is currently not an ability to have students work in pairs or teams to code on a given project. Things like Visual Studio Code have the ability create live sessions for multiple team members to code on the same project, so I would imagine it's possible for MIT App Inventor to do something similar. This is something that I would like to see for students to learn as teams.

You can use http://code.appinventor.mit.edu/ .
It has login with code feature. Anyone having that can login to a particular account and work on projects. But, only one active session at a time.

Right. But that wastes time in class when I could have all students working simultaneously. Single login is not efficient and is not conducive to team/pair programming principles.

It sounds like you don't want pair programming in that case. In traditional pair programming usually one person is the navigator and the other person is the driver. It sounds more like what you want is realtime collaboration a la Google Docs. We have an experimental server where we've explored this functionality for App Inventor. The challenge is that because block environments attempt to prevent any syntactical errors, getting the semantics of realtime collaboration correct with blocks is harder than in the text based case, where you can just let the programmers deal with the errors.

You are looking for Code With Me feature. It is available in Intellij products including Android Studio. Now, how different Android Studio and AI2 are, that's we all know.
See if there is any other approach which is suitable in your case.

That's understandable. There is already a show warnings feature and if programs don't run correctly, they error out already, so I am less concerned about that aspect than I am about real-time editing.

Being able to stick 2-4 students into a group to code a project would make everything far more efficient and really achieve the goals of getting students to operate in more independent code environments, such as building individual components as a team in Jira/GitHub or another platform for group work.