Jorgen, I do agree that at the A7s's price range this camera has a LOT to prove, but I have to say that even though I don't want to start a peeing contest, I don't have a single customers that would see your 12,800 sample as usable. It's really REALLY WAY worst than the A7s's sample. I could throw all kinds of technical mabo jumbo at my customers to try to justify why the GH3 or the GH4 might be a better camera because of this or that reason, but at the end of the day you're getting paid for the results you present and at the moment I cannot see ANY micro 4/3 camera that can be used under REALLY poor light for professional work.
None of those cameras are really useable for professional work at ISO 12,800 judged from the samples above, but the message Sony sent out when the A7s was launched indicated strongly that it was. The GH3 photo was btw. taken under a very yellow/orange street light, so the colours are totally off and would have to be adjusted individually to get anywhere near correct colours. Unfortunately, it's the only ISO 12,800 photo I have available taken with that camera.
However, by using one of the f/0.95 lenses for the Panasonic, one would constantly be 1-2 ISO stops lower than with the Sony, so ISO 12,800 with the Sony would mostly be 3,200 or 6,400 with the GH3, which is now a $1,000 camera. The difference in price to the Sony would buy me 2 of the f/0.95 Voigtl̈änder lenses or the PanaLeica 42.5mm f/1.2, all extremely solid performers and all native m4/3 mount lenses.
I've been holding back m4/3 purchases lately to see what I could gain by going the A7 route. From what I've seen so far, it seems to be a pointless exercise in my case unless I need a 36MP camera, and I can as well start selling off my 35mm lenses and go all m4/3, adding a GH4 and more lenses to what I already have.