I personally would like to see a Retina version of the Mini, even it has to be thicker and heavier. Pundits who claim Apple made a mistake launching a thicker and heavier RP version of the iPad don't understand or appreciate engineering. Simply keep the current version of the Mini around and let consumers choose.
Of course, Apple might surprise us with a RP-Mini that is neither thicker nor heavier. That would be a remarkable feat of engineering.