Since it is very unlikely that the next Mac Mini (and the next Macbook Air) will be "4K-ready", I wonder if Apple will release two types of new Thunderbolt Displays: one with the current resolution (hopefully at cheaper price) and one with 4K resolution?
Haswell Mac Mini (current design) + cheaper Thunderbolt Display (+ USB 3.0) would be my perfect combination!!!
IMHO I think it will be 4k ready considering there will be at least a 2 year refresh period and all the other minis are coming out 4k ready. The OS will be 4k ready in the next release. It will require TB2 and PCI for 4k. How Apple deals with that could be like other minis with msata and a bay for sata3 expansion. I don't see a refresh or redesign until IMacs are TB2 and all PCI.
But it is all speculation.