Besides the obvious 2013 Haswell update as soon as Intel is ready, what if Apple also released an ARM based Pro? A blade format multi-chip solution with up to perhaps 16 chips with 16x4 cores, something like an A7?
If Apple were to do the next gen development in the Pro form factor, it would support legacy and future peripherals better than some sort of all-in-one as a dev platform. The advent of ARM based server farms demonstrates it is real and practical right now.
Initially it could also have an Intel chip so you have a boot instance of Intel OSX and a "server farm" inside the box running instance(s) of OSX (iOS) for ARM.
A Haswell chip is going to cost Apple between $350 and $1000 each raw cost. ARM chips cost them under $30 raw cost. So 10-30 A7 chips per box is not price out of bounds.
Rocketman
https://www.macrumors.com/2013/03/1...r-20-nm-a7-chip-with-early-2014-availability/