Certainly does sound like a fun product that could possibly kick serious butt!
However, for those looking away from Sony's recent A7/r ...
What's the register distance for the A7?... is it short enough to handle adapters and a variety of other makers lenses? If so, makes a very versatile imaging back end compared to an F-mount.
Yes, it can handle adapters for Nikon, Leica, Canon etc. There are already videos on youtube of people testing pre-production models with 3rd party lenses, such as the 17-40L, with working autofocus. Also, Samyang has announced that they'll be releasing 5 lenses for the Sony FE mount (14mm f/2.8 ED AS IF UMC, 24mm f/1.4 ED AS IF UMC, T-S 24mm f/3.5 ED AS UMC, 35mm f/1.4 AS UMC, 85mm f/1.4 AS IF UMC).
Also, given that Sigma has their lens mount swapping service, I wouldn't be surprised if they came up with their own FE mount.
In reading comments here and other forums regarding the new Sony body, I do not think people realize how crappy AF performance is going to be using other lenses than the new Sony lenses.. That realization along with the plethora of older 3rd party lenses will mean - manual focusing - which is even crappier using an EVF.. Mirrorless bodies are neat and all, certainly a means of access to more lenses than any one manufacturer ever dreamed of, but it is of limited benefit and not a functional substitute for an OVF and dedicated AF sensor.
As for the excitement over body size... all any manufacturer needs to do is drop pop-up flashes, drop 3.x" displays, drop the gadgetry that provides no benefit to actual photography (GPS, WiFi, etc) and maybe even ditch video recording (though that does not effect camera size other than another button, but is less than ideal with a ~2" lcd) and there would be plenty of room to shrink the body size around a FF sensor, mirror, and OVF.
In reality it is the average consumer today wanting any gadget they think will take the photo for them and tell everyone else they were there that prevents manufacturers from producing small foot print DSLRs - - NOT the current technology.