TLDR:

• I went to quick in soldering and maimed one of the two interleaved ADCs;
• Interleaved mode works!
• Biaising my signal by Vref/2 is not working. To solve.
• Am trying macrofab for small scale production!

I was still able to get a good ultrasound image with this ADC (see my other project on ultrasound imaging dev kit blog post):

For general info, here's what the GPIO memory looks like during 10k samples at 10MHz =)

and here's what 2 ADCs normally interleaved produce when one the ADCs has two output pins soldered together:

At least I still have one ADC to play with, and experiment!