A number of resellers have run dry of Apple Thunderbolt Display inventory, suggesting the 27-inch monitor may be due for an upgrade, perhaps with a thinner design that takes cues from the latest iMacs. As of Monday, major resellers Amazon, MacMall, and J&R are all out of stock of the Thunderbolt Display. Stock-outs are often one of the first signs of a forthcoming upgrade to Apple hardware.
A new Thunderbolt display could take on a design more similar to the new iMac. It would likely incorporate the new MagSafe 2 connector and could gain USB 3.0 ports instead of 2.0 ports. The new iMac is thinner in part because Apple fused the LCD to the front glass. This advancement would also likely be applied to an updated cinema display.
For the hopeful, there is a small chance that Apple could release a Retina Display.