So is it confirmed then that multiple libraries will not be readily supported in the new Photos OSX like they are in Aperture? This was one feature I really loved for helping to keep our massive collection of family photos manageable. I used to use iPhoto, but as the library grew, iPhoto bogged down.
Not at all. Nothing is confirmed yet, because there is only a Beta version being tested, and Beta versions can change any day, without prior warning
The current Photos Beta supports switching between libraries, but only one library can be the main library and sync with iCloud, just like you now can only have one Aperture library or Photo Library use the photo streams.
So, if you want all your photos in iCloud Photo Library, merge the respective libraries into one library. And do not include the photos that you do not want in iCloud.
I know that, but for iPhoto one could not switch libraries within the software.
iPhoto 3.6 has a "Switch to Library" in the File menu, just like Aperture, also "Open in Aperture".
In Photos you double-click the library you want to open.