Ok, I have the facts!
There is no active capping on the number of files, but we do have recommended limits - these are the quantities we’ve tested to and are happy will work fine.
For Uniti players/Naim streamers, we’d recommend around 1000 albums/10,000 tracks
For Uniti Core - a more dedicated music-management device - we’d recommend 10,000 albums/100,000 tracks