Pretty sure they are both going to be exactly the same. The most important think is to make sure whichever route you go for get a decent calibrator. Either that or get a dedicated screen from Eizo or NEC. They come with matt screens and the CG or Spectraview models come with calibration software. Are you a photographer or designer?
The NEC ships with a HDMI to thunderbolt cable and will work with the iMac just fine. I think you have to pick up an adaptor to use the Eizo but it's not that much.
The new lamination process for the new iMacs means they're actually better than the older Cinema Display/Thunderbolt displays. I expect we'll see updated Thunderbolt displays at some point.
The new lamination process for the new iMacs means they're actually better than the older Cinema Display/Thunderbolt displays. I expect we'll see updated Thunderbolt displays at some point.
You have both options: you can mirror your iMac display or use it as a secondary display (extended mode). You can even make it your default display (with the menu bar and dock on it).
I think that they'll split their display lines. The new MBA only supports up to 2500px, which perfectly fits the current Thunderbolt Display. The new Mac Pro will support 4K and I expect that the next 15" MBP will do as well.
So I doubt that they'll dump the Thunderbolt Display and leave the MBAs behind with no external display solution.
My guess is that we'll see an updated TD in the new iMac's design, using the same display technology. And a new Cinema Display with 4K for the pros. At a ridiculous price, though.