Apple HDTV would make more sense as a huge upgrade to the little AppleTV box. TVs are very long lasting devices, our main HDTV is over 10 years old, and there's still little reason to replace it. A new one would be far thinner than the big projection TV, but there's no other reason to change.
A touchscreen television would be stupid. Fingerprints, not to mention that's why we invented the remote control! I remember having to get up to turn the dial, and that wasn't fun even when there were 13 channels. Visually, being a foot from a HDTV to touch the screen would be pretty hard to choose and see what you were doing. No touchscreen TV's please.
But selling a small box that has the smarts for the TV does make sense. With a cable input and DVR type stuff so it can watch and record live TV--or just be smart and if I COULD have recorded it, let me watch it over iCloud.
OnDemand from the cable company is nice, but channels can be so stupid--I didn't watch the Walking Dead in the narrow window when they thought it would be OK. I watched the first episode, then by the time I came back only the last few were there. So I gave up and watched other things...because of that time limit they've permanently lost a viewer.
Siri for voice controls, it wouldn't even need a remote at all much of the time. A UI just the same as how you have icons for apps now, but they'd be icons for channels or for a show. ABC/CBS/NBC/Discovery icons, folders for Sports, Movie channels. It could show a name & picture for each show in the icon on the screen too; the little number in a red circle if there are new episodes. The ability to add and delete channels and shows from your home screen to move them around as you want would be awesome. I could setup one page worth of stuff that are the ones we really watch, scroll over for the others. And just be smart and put the things there that we DO watch.
A little remote like the current AppleTV's would work to make sure something is always there in the room, directional arrows to choose between the menu...but connecting to use any iPhone/iPad would be better. It could mirror the UI to just tap the channel to use. (A few arrow presses in a grid would still be fewer than browsing the long list in the current TV)
That sounds like something Apple would do.