These new FF mirrorless cameras are certainly interested, but I'm with the crowd who is yet to be convinced. The main thing which attracts me - and most other people I think - to mirrorless is having a lighter and somewhat smaller camera. All the excitement about the Sony's got me interested in their weights so I came up with this comparison:
Sony a7 475g v Canon 6D 800g (with battery and memory card)
Sony + 35 f/2.8 595g v 6D + Canon 35 f/2 IS 1135g (Sony weighs 52.42%; 540g lighter)
Sony + 35 f/2.8 595 v 6D + Canon 40 f/2.8 930 (Sony 63.98%; 335 lighter)
Sony + 55 f/1.8 755 v 6D + Canon 50 f/1.8 930 (Sony 81.18%; 175 lighter)
Sony + 24-70 f/4 OSS 905 v 6D + Canon 24-70 f/4 IS 1400 (Sony 64.64%; 495 lighter)
Sony 70-200 f/4 OSS 1315 v 6D + Canon 70-200 f/4 IS 1560 (Sony 84.29%; 245 lighter)
Sony 70-200 f/2.8 SSM 1975 v 6D + Canon 70-200 f/2.8 IS 2290 (Sony 86.24%; 315 lighter)
So, the Sony a7 saves up to 500g (50%) at the shorter FL, dropping to around 300g or less (15%) at the longer FL. The a7 kit ranges from 600g to about 2kg, while the 6D kit ranges from 1kg to over 2kg.
For the weight savings of the Sony, I have to give up an OVF (I guess some may saying I'd be gaining an EVF, but that's not how I see it), and I expect some battery life (I'm assuming that because of the OVF). And I would currently have a very limited "native" lens selection (will have to see how well adapters work to enable use of other lenses). And is there anything else I'd be giving up too? Ergonomics? AF? I guess we'll have to wait until people have the Sony's in there hands and we get some "real world" info. (And yes, I'm well aware the 6D's AF has it's limitations! But still, the question remains how the Sony's AF will compare.)
Like I said, the a7 and a7r are interesting. I'm looking forward to hearing more once people have had time to shoot with them for a while. But I remain to be convinced!
And for further comparison:
Olympus OM-D EM-5 430g v Canon 6D 800g
EM-5 + Olympus 17 f/1.8 550 v 6D + Canon 35 f/2 IS 1135 (EM-5 48.46%; 585g lighter)
EM-5 + Panasonic 25 f/1.4 630 v 6D + Canon 50 f/1.8 930 (EM-5 67.74%; 300 lighter)
EM-5 + Olympus 12-40 f/2.8 812 v 6D + Canon 24-70 f/4 IS 1400 (EM-5 58.00%; 588 lighter)
EM-5 + Olympus 40-150 4-5.6 620 v 6D + Canon 70-200 f/4 IS 1560 (EM-5 39.74%; 940 lighter)
EM-5 + Panasonic 35-100 f/2.8 790 v 6D + Canon 70-200 f/2.8 IS 2290 (EM-5 34.50%; 1500 lighter)
So, the EM-5 saves generally saves at least 500g (close to 50%) at the shorter FL, increasing to around 1.5kg (65%!) at the longer FL at f/2.8. Or if you prefer, EM-5 kit ranges from 550g to 800g while the 6D kit ranges from about 1kg up to well over 2kg. Sure, the EM-5 has a smaller sensor which will give up some IQ under some conditions but still, if weight (and I assume size) is your concern, the EM-5 offers a substantial gain to offset whatever else you lose.
I think if I could afford it, I'd have a 5DIII and an EM-5 ... but for now I think I'll just be sticking with my 6D (and my old 7D).