The device has the model number A1844, which is not currently in use by any Apple device. The power supply and screw placement are in line with the existing Apple TV, although not perfectly identical.
The timing would make sense, as Apple has traditionally held a second event in the fall, post-iPhone, to release a few new devices. This year, Apple watchers expect to see new MacBooks as the cornerstone of that event, but an update to the Apple TV is very possible.
Along with a few technical details for the device, Apple also submitted documentation for testing Bluetooth and NFC radios in the device. The inclusion of NFC is a little puzzling, as Apple has so far ignored the technology, only using it for Apple Pay in iPhones.
There's no Wi-Fi radio mentioned, but that doesn't mean much. Assuming this is an incremental update to the Apple TV (a safe bet, as Apple doesn't normally let brand-new products leak through the FCC), it would use the same Wi-Fi chip as the previous version, and not require re-testing.
So what new features can be expected? The 4K HDR video is a notable omission from the current Apple TV, and with new Playstations and Xboxs emerging with 4K capabilities, adding that in would be a smart move by Apple.
Less likely is the addition of more smart home technology. Some kind of Apple competitor to the Amazon Echo has been rumored for a while, and the Apple TV may well have a role to play in Apple's quest to take over everyone's home. But a small, incremental upgrade to the Apple TV - which is what this looks like - probably won't be the cornerstone of Apple's smart home plans.