I doubt you’re going to see significant internal storage. What would be ideal is if they allow you to hook up a USB or networked (e.g., NAS) drive and have an iTunes client run directly on the ATV rather than relying on an intermediary like a PC, Mac, or iDevice to be the iTunes client.
Honestly, I think they really need to take a good hard look at iTunes anyway - it needs to be split, at a minimum, into a server application to manage the library and a client application to use it, allowing multiple clients to use the same server and see updates made to the library from any source. That applies to not just Apple TV devices, but multiple PCs/Macs and multiple users on each computer as well. No reason a hosehold shouldn’t be able to share one centralized library with independent views into it. Home Sharing is a little to clunky to count as a real solution.