Jack March reports:
A source familiar with Apple’s plans tells me that Apple is indeed planning to launch a Retina iMac at their next press event, however the 27″ Model will be the only model that gets this feature.
MacRumors has a roundup of other sites that are hearing the same.
As discussed on a recent episode of the Accidental Tech Podcast (at the 5:10 minute mark), this doesn't necessarily mean that we will see a Retina Thunderbolt Display soon. Displays in the iMac and MacBook lines aren't subject to the limitations of a cable connection, such as Thunderbolt. Because of its more powerful bus setup, only the Mac Pro could support a Retina Thunderbolt Display at this time.