I wish people would understand how electronics (especially in computing) works. The A5 was installed in the iPad mini on purpose because they'd refined the chipping process to package it as a smaller chip, using less power and being perfect for the iPad mini's 1024 x 768 display. That's why it took so long for us to see this version of the iPad to appear.
As a minimum, the A5X is needed to run the retina display. Hopefully this time next year, they'll have compacted the chip to be much more effecient and a lot smaller. The new screens should hopefully need less power than it's iPad 3 cousin running the same chip. It's very possible they'll be no sacrafice to the battery life for these reasons.