Dropbox is rolling out support for Google Docs, so you can create / store / edit Google Docs files in Dropbox. It's an opt-in beta feature at the moment, but hopefully it will roll out quickly.
Just wondering about Rclone support here, specifically:
supporting Google Doc files on Dropbox remotes; and
supporting copy / sync / move of Google Doc files from Google Drive remotes to Dropbox remotes
I'm guessing Rclone won't support this right now, but hoping Rclone can add this functionality now that Dropbox is rolling out this change.
It's possible, but they would also have to expose it via the API. Best bet is to create a feature request on the github if it is something you are looking for.