There was a regression (at least in 8-STABLE) a while ago that caused the "still waiting" message, but it was fixed within a few weeks at most. That seems unrelated to the linked zfsguru topic, as I ran into it on an Adaptec ahd(4) controller.The system arrived and:
View attachment 2468
The send a new controller however the situation is the same.
Since it only (from your screen capture) appears to be happening on unit 10 on the mps1 controller, I'd suggest removing that drive and seeing if the boot completes. I think you may have a bad drive.