Is this possible? Maybe with Dropbox Business?
What I do:
I have a desktop that I render architecture scenes on. It has tons of storage.
But I also have a laptop with limited storage that I set up scenes and work from. I'd like to keep my most-used Dropbox folders on my laptop interal drive for when I'm on the go. But then put my hundreds of gigs of rendering assets on an external drive and have it sync via Dropbox so that it's always up-to-date on my desktop that I actually render on.