Not to be a wet blanket, but I think there are a few things that Apple TV 4 will not have:
1. No recording. I have a strong feeling that the last thing Apple would ever want Apple TV to do is to record arbitrary content from sources they don't own. There are already tons of DVRs out there. No need to add a me-too product that's just slightly nicer than the current pile of DVRs.
Also, Apple has worked for more than 10 years on the whole iTunes infrastructure. And they'll be working for the next 10 years on building out iCloud. The Apple TV 4 will need to leverage all that hard work and prepare for the next decade. And that means streaming live, rented, and purchased content. Not recording some other provider's content. Apple has eliminated the floppy drive, they've nearly eliminated the CD / DVD / Blu-Ray drive, and now they're targeting DVR recording features.
2. No cable or satellite input. There may be a brief interim period when Apple caves and does deals with a few US-based legacy cable and satellite providers. But aren't there hundreds of them around the world? Wouldn't it be a big ugly contractual furball to try and get them to all sign deals?
I think cable and satellite networks are on their way out. They're very hard and very expensive to extend, whether it means more copper / fiber cables or more satellites. Either technology is costly and trailing-edge. I think the cell carriers, if and when they roll out "real 4G," will be able to step in and replace cable and satellite.
How? By delivering 1Gbit/sec to stationary and slow-moving devices (e.g. walking around) and 100Mbit/sec to fast-moving (auto, train) devices. The ITU 4G requirements include those download speeds. Why bother with wires or satellite dishes if your cell company can stream video at 1Gbit/sec to your Apple TV 8 (or 9 or 10 or some future product.)
Of course, there are a lot of big "if's." If cell companies can actually implement 4G (after the current LTE networks are fully built out), and if 4G really delivers data fast enough to watch video on any device anywhere, and if Apple can do deals with all the TV and movie studios, and if the cell carriers want to do deals with Apple, and if the cell carriers don't enforce money-grab data caps, ad nauseam.
Whew. Well, maybe that went a little beyond Apple TV 4. But I just can't keep myself from thinking long-term.