What I'd really like to see is a WebRTC type interface that overlays this to provide some kind of collaborative environment on top of it. I'm thinking of a built in voice chat as well as multi-author editing within the same codespace. Imagine it like pair programming. I'm in FileA.ts and I can see a little avatar icon of another dev in FileB.ts (maybe surfaced through the Explorer and/or the file tab bar). The voice chat could even be location aware so if we are in the same file/package then we are able to chat. I'd go so far as to allow multiple editors to affect the same file within the codespace so I could see the other dev edit the file in realtime (like coderpad or other interview tools).
I imagine a workflow where a feature/ticket is mapped to a codespace. One or more devs are assigned the codespace and they work together until the feature is completed. Incremental changes are stored up until a "build" action is submitted, resulting in the current contents of the codespace being built and deployed to an internally/publicly accessible endpoint. This might also result in a "snapshot" which could represent a commit to a sandboxed repo. The codespace goes away once the feature is completed resulting in a single check in to a master branch which would go through regular code review type processes (probably a squashed version of their local snapshot's changes).