I am sure (well actually not really!) that if Apple announce a Retina or 4K iMac then they will also announce a Retina Thunderbolt display. I think they have to really? If they don't then where does this leave the MacPro users? They would be left with the option of running a 3rd party 4K display? - if they want/need 4K. Whereas a 4K iMac would have (no doubt) a purpose built display that works in perfect harmony with the entire computer. No refresh issues, not font size issues, no scaling issues, just perfect harmony. I really really (really) want a 4K Apple display and as my current MacBook Pro Retina (15 inch Mid 2012) probably won't be able to run it, I am also considering buying a new MacPro. But if the 4K Thunderbolt Display does not appear, and the Retina or 4K iMac does, then I would likely buy the 4K iMac. If Apple had released a new Thunderbolt Display back when they released the new iMacs, with a similar form factor and USB 3.0, then I would have bought one for sure. But now with 4K in the picture (maybe) that's what I want.