Lens systems are a major barrier to moving into a new format where competitors are already well established; both the need to design an extensive new array of lenses, and the fact that many people already own lenses for another system in that format. This works the other way too, and is one reason why I think there is very little chance of Canon or Nikon launching a system in a format larger than 36x24mm, or of Pentax or Olympus returning to 36x24mm format now that they have few or no up-to-date lens designs for that format.
It depends on what you shoot. I seem to get the feeling that a lot of A7r buyers are buying adapters for their Canon lenses just to get 35 mpx.
For someone like me who uses and needs fast autofocus I'd probably go the A7 which means A mount lenses, to cover the range I have with Canon and if I compare Sony lens prices to my Canon lenses, I'm at around $9,000. If you go that far into a system you need two bodies, two adapters, two right angle grips so to make a change from Canon to Sony is $14,000.
Digital film gets expensive.
There are a few things I'm missing on this system. Why does the 7r sync at 25oth, the 7 at 160th and why not the same focus sensors on both AND why can't they cover 80% of the frame like the olympus em-1?
I think it's a nice camera, but it really seems rushed. For most I don't think it will stop the sales one bit as they'll either use their own canon lenses and adapters, or buy a couple of the slower e-mount lenses, but if you work professionally, the numbers change drastically.
As mentioned Sony needs a CPS type of service if they're really going to make a dent in Canon and Nikon. I can send my Canon in for a shutter on Monday, get it back on Thursday at the latest for a low price.
Use to I'd say they need to increase their rental presence, but give that lensrentalsdotcom and borrowlensdotcom exist, the usually cover most formats and brands, so at least their is that option for the one time in two years you need a 400mm lens.