I think the interesting questions are:
Well, I don't know. I think I have some slight different opinions on this.
1) When will Apple introduce a Retina Thunderbolt Display with 4K resolution (3840x2160)? My guess is it will be announced when the new Mac Pro becomes available to order.
I don't think Apple will release it with the new Mac Pro for the following reasons:
A 3840x2160 display should still be very expensive for mass production (look at the prices of all these ultra-high resolution TV sets). Apple won't be able to cram a 3840x2160 resolution in a display with the same quality as the current Thunderbolt displays and sell it for US$ 999, or even US$ 1,999.
What size would be the display? If the display has the same 27" as the current 2560x1440 display, than (i) Apple would have to make it a retina display and then the real estate will be actually lower than the current model; or (ii) the real estate would be very high, but pixels would be very small. I don't think Apple will release a larger screen than 27", because that would make it really hard for using it.
Which video card would drive such high resolution? An NVIDIA high-end card could handle it for daily tasks, but the Mac Pro is supposed to use the full power of these video cards for some real work, and not for just making a smooth web browsing experience.
The Thunderbolt display has the same display as in the iMac. Apple could release new Thunderbolt displays to match the new iMac displays (e.g., less brightness). But I don't think a higher resolution will come right now.
2) When will iTunes movies become available in and an updated Apple TV support movies in resolutions above 1080p, such as 1440p or 4K? My guess is that probably is being delayed by contract negotiations with the content providers.
Perhaps it is under negotiation. I don't know if it's being delayed. I guess there just aren't too many devices so far to make use of it so it's worth it.
My questions are a little bit different, and perhaps simpler:
(1) When the retina MacBook Air will be released? I guess next year, together with a redesign.
(2) When the retina iPad mini will be released? I guess next year as well, but could well be later this year.
(3) When the retina iMac will be released? I guess with the next redesign, in some 2 or 3 years from now.