Yeah, I imagine it will work in future betas. For now I'm just sorting the faces out on both my iPhone and iPad so that I can use the feature on both.
[doublepost=1466018030][/doublepost]Update: I just finished sorting faces from a library of around 2500 photos on my iPhone. I use iCloud Photo Library so this is the same one I sorted on my iPad this morning. Anyway, I noticed that while the recognition was mostly the same, there are a few faces recognized on the iPhone that aren't recognized on the iPad and the total number of photos under each person are the same for most people, except a few.
This has made me come to the conclusion that because the actual facial recognition is done locally on each device, the results are going to differ slightly from device to device and therefore it cannot sync because each device has different results. That's my guess. It could very well be a feature that isn't yet implemented, but I think face recognition syncing is not going to be available due to privacy.