You can install photos app through play store.
The app icon doesnt appear in the list of apps. I opened the app through settings. Configured my google account but pics are not appearing.
Even I can select photos app and google acc. in screensaver but not showing any albums/pics.
It might be connected to google drive and may require a syncing service that has been disabled for androidtv (just a total guess)
I did this earlier today on a MI box. It took a couple of minutes before the images started to show.
I just used photos app for screensaver. Its working great. I can select the albums which I want to display.
FYI - The reason that photos may never be fully supported is that many people don't want every person in their living room to have access to their entire photo library.
Android Phones and Watches are designed around a single user having control of them any time that user is signed in. Android TV will probably never get a number of apps like photos, gmail, G+ and any number of other apps. It's the same reason that facebook hasn't released an app for browsing your feed on TV.
I don't know what exactly you're trying to do, but download TV App Repo . It lets you create leanback launcher shortcuts for sideloaded APKs.
Also if you're looking for a good screensaver, Aerial Dream is amazing.
I'm interested in that also