Have you tried adding the kernel parameter "mem_sleep_default=s2idle"? I know you specifically asked about "deep" but I just want to make sure you are aware of this. I've got access to MacBookAir7,2 and this option allows the sleep, I think (keyboard backlight still stays on) but I can't ping it nor does a process continue processing but maybe it's not fully asleep still, I'm not sure. That and installing "bcwc-pcie-git" and "facetimehd-firmware" makes these great machines!