Is it possible to: turn on iCloud Photo Library, open one library, let that library upload entirely, quit, open your other library, let that upload.
At this point wouldn't all photos now be in iCloud, and you can delete/let stuff download however you want?
Or do I remember seeing something about how only 1 library can use iCloud at a time?
Yes I was thinking this also.
I used it in beta and only recently added it to my iMac which has my main Aperture Library. One day I want to Merge Aperture but I am not ready yet because I have to sort it a bit first.
I have not tried yet but here is direct quote from the Photos Help
"You can switch to another library and designate it as the System Photo Library. If you designate a new System Photo Library, you must turn on iCloud services in Photos preferences again. When you turn on iCloud Photo Library after designating a new System Photo Library, the photos stored in iCloud are merged with those in the new System Photo Library. Once the content from the new System Photo Library is uploaded to iCloud, the libraries cannot be unmerged, so it’s a good idea to consider carefully before changing your System Photo Library."
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