I have a strong suspicion that Apple is working on a new industrial design for the Mac mini, a taller one with a smaller footprint (like the AirPort Extreme but in aluminum or maybe something like the new Mac Pro). If Apple just wanted to upgrade the internals with the same mini pizza box chassis, they could have done so months ago. Of course, this is pure speculation on my part, without a shred of rumor/evidence for me to work off of.