Just a quick follow-up to this. I ran into the same things again with the upload that made me pause before, and I forgot about it (again). I don't always have embedded coverart. I do not want to add it because that would require all of these files to be re-uploaded to Google Drive.
So I just made a new library with G:\ as the import path - I selected a sub-folder so it wasn't the full few TB of data to play with. JRiver and Google Drive File Stream seemed to play pretty well together. When the import ran, it seemed to re-cache a bunch of files. I saw a good bit of downloading occurring, I think it downloaded everything that I imported again, but just temporarily. My drive fluctuated between 500 and 480 gig free, so it may have downloaded 20 gig at a time, then purged it.
I just hit play from a remote location on my Mac, with the G Drive Library loaded on my MC server. I was able to stream music from Google Drive File Stream, through MC on Windows to my Mac remotely, while the NAS is off. Thought that was pretty neat.
I'd love for Cloudplay to do this, but changing my library to meet the requirements is just too big of a hill for me to climb. Not to mention, how would I keep track of what was uploaded and what wasn't, without just re-uploading everything? I accomplish this with Free File Sync to Google Drive. If a file hasn't changed, it doesn't re-upload it. If a file is new, it uploads it. Something similar with Cloudplay would be amazing. Perhaps you could even check FLAC fingerprints without metadata tags so that those changes wouldn't trigger anything. That would be killer.
I'm happy to keep trying different approaches to this, but the embed coverart requirement is really annoying (to me). I play the music in MC and see coverart, so I think the uploading agent should too.