I think either we'll see a a99 successor that records 4k internally for double the price of this camera, or we'll see a A7S successor next year with 4k internal recording, depending on how the competition goes. Or maybe something in between? Small body, 4k internal, same HDMI options from A7S for US$2500? They can't depend on external recording forever if they wanna sell those 4k tv sets, right? Not if Canon comes out with full frame with internal recording.
I guess the best option is to get GH4 now, and see what happens next year.
For the price of a GH4 + YAGH (whatever the hell that thing is called) + recorder, or for the price of A7S + Atomos recorder, maybe it's a better option to get GH4 + A7s and cover all your needs. Something tells me that if you buy a 4k recorder now for a A7S, you're gonna be very sorry in 2015.