Right now most of us we are going to shoot 1080p for a great many projects and the A7S wins this battle hands down. On paper it looks like the most complete 1080p DSLM ever made, it offers almost everything we have ever asked for... So many, real world, filmmaking capabilities such as full-frame, APS-C, extreme low light, no nonsense decent codec (50mb/sec for 8bit 4:2:0), S-log picture profile, no need for expensive adapters, even 120frames slomo in 720p(by now obsolete...) and uncompressed output (yet only!)8bit 4:2:2.
However, most people argue about the lack of internal 4K recording!
Obviously 4K is the future but untill our workflow gets properly 4K with respective monitors, PCs, GPUs, TV sets etc. this camera is going to be king for the budget, indie filmmaker. I believe 4K needs a couple of years before it gets industry standard, yet people are already sold to it before they have or can even use it. We've already seen cameras that promise the future and do not deliver now(Blackmagic anyone?) and when the future comes they are already out of specs.
Don't forget that next year GH4(another excellent offer) is going to look so... well, last year. Such a shame really!