No way they can achieve the necessary margins
I just don't see how Apple can achieve their desired profit margins in the TV market. Displays are a commodity market in which the premium on new products lasts for 18 months at most. And, the purchase life cycle on televisions is 3-5x that of laptops, let alone mobile phones. I have a TV that was very expensive when I bought it...13 years ago. It is still going strong, outmoded only by its lack of HDMI.
For a TV to work from a profit perspective, Apple would have to accept lower than usual margins and then make money off the content being delivered to the TV. Even there, I see problems. I doubt that many people want the smarts built into their TV; the set-top box/display combo is much more flexible and easier to upgrade. There is a reason that Apple TV and Roku do their thing for $99 and pass through any subscription fees. The main thing lacking in the streaming content area is unification: there are too many sources to which I have to pay too many fees and use too many different devices to access. But Apple hasn't been able to fix those problems so far; attaching a 4k screen to them won't help.
And, how many people have been burned by the automatic software update that changes or eliminates a feature that they used to like? I personally wouldn't pay a premium for my television to be locked into whatever decisions are made in Cupertino about changing the UI, licensing issues with this or that studio and iTunes, and so on.
Maybe Apple will surprise me and come up with a truly innovative product in this space that makes me want to spend extra on their brand. But, I'm skeptical.