Mac Photos app stuck on "Restoring from iCloud"
Since I ran into the same issue, I had to research this as well. From what I found, this seems to be normal. After a library repair, each photo is being verified against the iCloud library copy.

This Apple support document 1 states:


  If you repair a library that's automatically updated with iCloud Photos, the entire contents of the library re-updates with iCloud after the repair ...


Just like a normal iCloud library upload, this can take a very long time. For my 20.000 photos, it's currently at 72 hours without an indication of being finished any time soon it took about 80 hours. Then, the Photos app showed Updating (only the word Updating without any additional information) for a few hours before now switching to Uploading 19,800 items.

It's re-uploading every single photo in my library. Due to my low upload bandwidth, this is a very slow process and it uploaded about 1,000 photos in the previous 4 days.

So for me the messages that showed up in the status bar were, in order:


Restoring from iCloud (for about 4 days)
Updating (for a few hours)
Uploading x items (very slow, will possibly take many weeks to finish)


UPDATE Jan/10: I took the laptop to work because we have a very fast upstream connection there. Over the weekend, it uploaded all photos, downloaded the new ones and is now back to its old Updated Just Now status.