Google Drive (the web app) does something similar to this (at a high level anyway). You can open a file from the Drive website in Photoshop, Word, etc and make

Google Drive (the web app) does something similar to this (at a high level anyway). You can open a file from the Drive website in Photoshop, Word, etc and make changes with your desktop software and when you hit save it is actually saving the cloud copy. So the file stays in the cloud but you can use any local software you like or need to be productive. I believe this uses a Chrome extension at the moment but extensions are also web based for the most part so the idea is solid.