A successor to Apple's current desktop display is more likely at least 7 months out. Look at the historical data: ignoring the outlier, Apple releases a new screen every 25 months - we're 18 months in. The last update was timed so because Apple switched from Mini DisplayPort to Thunderbolt.
As for Apple releasing a TV screen, I don't see it happening for at least a couple of years, if ever. There are too many things that need to be in place for Apple to be able to really change how people watch TV. For it to really shake things up, we need fast broadband everywhere, more (live) content in iTunes, a better input method (hand gestures? voice? touch?) to control the screen, and a more reliable wireless technology than (the current) WiFi.
Not to mention the state of the art hasn't moved very much - that 27" IPS LCD panel is still the very same that's being used by Dell, HP, et al.
There's been a lot of development on both smaller and larger screen sizes, but the 27" form factor seems to be at a relative standstill.
I don't expect to see an update unless there is a major change to either the panel tech or the interface tech. I really do hope that Apple reopens the >= 30-inch space though.
My pet theory[1] is that they'll jump to 4k/QFHD (3840x(2160,2400)) by using the same panels for a desktop Retina Display and as a stand-alone Apple TV. I think this would "shake things up" without having to sell in iPhone/iPad volumes.
A desktop Retina Display would be a great pairing with a Mac Pro replacement, which one might expect when Intel's Haswell starts shipping, which happens to be around 106 days from now. And they could retain the existing Thunderbolt Display as a lower-end model. (It also helps that Apple's current models all support outputting that resolution.)
A 4k Apple TV would allow them to differentiate from most of the TV market and soak up a fat margin in an area where only one of their major competitors (Samsung) as any position. And it wouldn't cannibalize the $99 Apple TV box in the process. There's still the chicken-and-egg problem of getting 4k content, but Apple, with iTunes and as a pipeline for Netflix, et al., seems to have a good position to get it.
[1] As a person so hip he doesn't own a TV or a Mac, yet finds the speculation irresistible.
I came by this information second-hand so I can't verify it, but I have been told that there aren't enough PCIe lanes going to each Thunderbolt port to drive a 4K panel at 60Hz. Which makes me as a rMBP owner super, super sad if it's true.
The 2011 MBP could drive two 2560x1600 displays (chained) through a single port, which requires about the same bandwidth as a single 3840x2160. So I don't think that would be an issue, though obviously the GPU is still a limitation.
I appear to be hellbanned from posting links, but I gather this from page 8 of AnandTech's review of the Thunderbolt display and the Wikipedia article for DisplayPort.
Shortly after that, Best Buy discounted them a bit ($50), suggesting to me they wanted to empty the shelves for new models (as they surely aren't automatic sales like iPads).
However, at this point I'm not convinced it'll be too soon, as whatever momentum the "signs" pointed to seems to have worn off.
http://arrival.io/apple-thunderbolt-display
As for Apple releasing a TV screen, I don't see it happening for at least a couple of years, if ever. There are too many things that need to be in place for Apple to be able to really change how people watch TV. For it to really shake things up, we need fast broadband everywhere, more (live) content in iTunes, a better input method (hand gestures? voice? touch?) to control the screen, and a more reliable wireless technology than (the current) WiFi.