Apple has never pushed Apple TV very hard, famously describing it as a 'hobby'. But almost since it appeared, people have been suggesting ways that it could be improved.
Updating the hardware to support at least 1080i would be a good start, and 1080p would keep even more people happy. Even if Apple never fits a Blu-ray drive or supports an external unit), people are likely to want to play full HD content obtained by other means. I suppose we're really talking about something similar to a Mac mini, but that's hardly an original idea.
Then add broadcast TV support. How much would it cost to buy Elgato? I've yet to see any sort of TV recorder with a better user interface than that company's.
My initial thought was to suggest redesign the Apple TV case so that a USB tuner can be attached without sticking out from the back (look at the way USB Wi-Fi or Bluetooth dongles can be added to certain HP printers for an example of how this can be done), but some of the latest tuners are so short that isn't necessary. External tuners save having to build different Apple TVs for different markets.
Revamping the Apple TV UI to provide access to Safari for web browsing is the next step, followed by adding a mechanism for configuring 'web channels' for simple and convenient access to YouTube and the various TV catch-up services.
What about the apps? See page 2.