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The renesas should work. Is almost the same minipcie card I've used, only difference is the power connector (mine is a sata powered).

I'm pretty sure any minipcie card with apple drives could be installed instead of the airport card.
Thanks for the tip @icpmac. I've just bought the card and will give it a shot and report back here. You're right about the right angle (or low profile) USB3.0 extension cable, that's hard to find. May consider a mPCIe extension ribbon instead.
 
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