Huff says the RX1 shows better high ISO quality, down to the SLT he thinks, and that is the a77/NEX experience. Most reviews are kind of overwhelmed by the feature list of this quality body.
I started a list of 'pros' vis-a-vis the a900 and almost ran out of paper: weight, grip, mirror slap, MUP, weatherproof, DR, video, peaking, high ISO colour retention, noise ceiling, GPS, LCD, EVF with image display/review, real time histo with exp changes, and exposure change on stop down, dual cards, 200k shutter...and some of these are industry or class leading, all of a sudden.
I see it being a much 'faster' camera - quicker setup, more shots in a shorter time, with less review need, for both tripod and handheld work. Which translates into more 'photography' prep time - composition, scoping etc. I hope they kept the shutter soft and quiet-ish.
I am all MF now, so I will follow what people find re the mirror. Sony service could do the removal most likely, if it's hard. Are there any function loss gotchas to mirror removal, outside of losing AF?
Jae, the AA is considered by several reviewers to be of 'moderate' strength.