A source just told me something very interesting. The current APS-C E-mount lenses like for example the Zeiss 24mm f/1.8 will work in two modes on the Full Frame E-mount A7 and A7r cameras:
1) Crop mode: It means you can use the lens like it would be attached on a NEX-5-6-7
2) Full Frame mode: It means you can use the lens with Full…Full Frame activated. I have been told some lenses will have a cool heavy vignetting effect and some lenses will also cover almost the full FF area. it could be useful if you want to use a larger than APS-C area (4/3 mode or so).
And now an interesting note for German readers: The Wallimex 24mm T/1.5 Lens for EF mount that usually sells for close to 7000 Eruo can be bought for 88 Euro(!!!). This is a FF lens so if you buy a 10 Euro EF to NEX adapter you can use it on your A7 or A7r! The deal can be found here: http://www.dealsrunner.com/deals/walimex-pro-24-1-5-objektiv-vdslr-fur-canon-und-adapter-pentax-q