I will be traveling without my Mac, but need to continue my editing. Can I edit using iMovie online? I would want to upload an entire (huge) library to googledrive or etc and work on it from any Mac, maybe in a desktop-rental place. If that is not possible: can I save a project online and then download it to use in my library? For example, I would take along a Mac, but I don't want to chance losing the edited versions if the Mac and any external HDs I bring along are stolen/damaged. If I don't need to import new events (nor move events, nor projects from event to event) while editing, can I save the newly-edited projects online somehow, so that even if all is stolen I can have the edited project back when I return home and re-connect any Mac to the backup HD with the iMovie library on it, so that iMovie will load with the project I had edited while travelling?
I'd recommend Dropbox. You'd be able to edit files locally with Dropbox, and then it would handle syncing them to the cloud. You'd just have to make sure you left your computer on long enough to allow it to finish syncing after you made changes.
I'm unsure if Google Drive works the same way - but I use Dropbox for something very similar to your scenario and it works great. I can edit files at home or at the office, and they sync across so I don't have to worry about transporting things back and forth.