Amazing special purpose lens which has a level of performance that is, IMHO, more than offset by the massive size/weight disadvantage for most applications. On the A7R I can only imagine it feels terribly imbalanced and awkward compared to, say, a 55 1.8 FE. That lens is so darned good and at 25% of the cost and weight. IMHO, handling has a far greater influence on good pictures than absolute resolution.
When there is a D900 with 50MP, I can imaging this lens being the best way of realising its potential, but how many people are getting the most out of 36MP?