Here's more info on the 4K FDR-AX1; some first impressions and videos that Sony has posted to YouTube. One important note about this beast: the camera uses XQD memory cards, and with a throughput of 150MB/s you'll need the S Series cards, which cost $199.95 for 32GB, or $299.95 for 64GB.
The Phoblographer | First Impressions: Sony FDR AX1–The First 4K Camcorder With an Auto Mode
See that XQD card in my hand in the photo above? It was burning hot when it came out of the camcorder due to all the work that the processor was doing. Since the processor is burning that hot, the system obviously needs a way to cool it. There is a fan in the camera where the intake is around the side hand grip and the vent is toward the back.
SlashGear | Sony FDR-AX1 4K Handycam official: top-quality video within reach
The exposure system on this device works with multi-segment metering modes and both AE level and speed compensation. You’ll have noise reduction, white balance modes for a variety of environments, and auto and manual iris control at F1.6 – F11.0. This system works with a minimum illumination at 60P : 4lux (1/30 Shutter Speed) (60P: 59.94P, 30P: 29.97P, 24P: 23.98P), or 50P : 3lux (1/25 Shutter Speed).
C|Net | Sony Handycam FDR-AX1, a 4K camcorder with $4.5K price tag
In addition to the affluent hobbyist, Sony thinks the camcorder might appeal to wedding and indie videographers. But I can't see it as an optimal wedding-friendly camera. What you gain in resolution you'll probably lose in dynamic range because of that 4:2:0 limitation, which can be a real drawback for all that high-contrast, tonally challenging wedding work.
IFA 2013 FIRST LOOK: 4K Handycam, Sony's first consumer 4K camcorder
Sample Video for 4K Handycam FDR-AX1
Promotion Video for 4K Handycam FDR-AX1
FDR-AX1, 4K camcorder