Forgive me if someone else has already brought this up, but what about dead pixels? For example: my 5D II has been aging pretty gracefully, but hot-and-or-dead pixels became impossible to ignore last year at the higher ISOs. When I bought my 6D, it had a few straight out of the box, but thanks to pixel remapping they disappeared immediately.
Direct pixel-to-pixel recording in 4K is going to mean that if a photosite dies, you can't get around it in-camera. And at the high ISOs where the a7S is so awesome, I think there could be a huge risk of the image being spoiled by these little buggers, and possibly sooner than you'd think, which will make high sensitivity shots a massive pain every time you go into your NLE.
I wanted so much to love the a7S—I think Sony is producing some of the best new sensors (D800, a7R, and yes a7S), codecs (S-log, XAVC), and all around cameras (I love the F55 and FS700 so much). Unfortunately, for my purposes at the moment, I think the GH4 is just a more usable day-to-day tool. I'll use the a7S when it's needed, but...
Anyone have any other thoughts on hot pixels with this baby?
@krisicwalsh