While pondering what it would take to have an extension that made it easier to sync work-in-progress across multiple devices, I wondered if the path forward might be more obvious if ST3 broke up .sublime-session state across per-window files.
These files (and the session itself) could be namespaced per instance and window so that different installs aren’t dueling over writes. Either core sublime or extensions (with some new APIs) could provide commands useful for listing each session, seeing activity, pulling in a window from another session, and diffing or overriding the state of a local window with a matching window in another session.