I view the Sony A7R as a surrogate, a sort of chameleon kit. It can jump from one systems bag to the next and fit in or be useful, but isn't a replacement.
I still have my A99 and all the FF A mount lenses from 16mm to 500mm. With the LEAE-4 adapter the A7R is part of that kit … however it is an Ersatz, because it lacks the IBIS, dual card capture, and fully articulated LCD.
The A7R can jump to the Leica M Monochrom bag and most of my M optics can be used for color work, or as a back-up. It falls short because it is not a rangefinder, so not a true substitute for that style of photography.
I can pop it into my Leica S systems bag with a couple of M or FE lenses as an emergency back-up. FF 36 meg helps mitigate the resolution situation, but is not a replacement for the MFD CCD look and feel, and doesn't offer a leaf-shutter solution when used with lighting. But, hey, it only takes up a slot that one S lens uses.
In its' own little 3 lens FE bag the A7R offers a nice tiny kit that really only needs a f/2 portrait focal length to be done for me. Nice travel option or general carry anywhere system.
- Marc