I really wish this was possible. Workflows using things like iZotope RX to clean up audio, often the best processing can't be done with plugins in realtime. And some audio editing just can't be achieved in S1. Being able to open a file in an external editor, edit, save and have it updated in the S1 timeline would be fantastic. It is essential for workflow in many situations. Especially when I'm working on sound design or podcast projects rather than music.
It would be great to take it one step further though. Have S1 automatically create a duplicate of the file that is sent to the external editor, retain the link to the duplicate so there was a way to easily revert to the original file if necessary.