It's fixed!
Picked up a used 24820-1MA2A cluster (for cars w/tech pkg) to replace the incorrect 24820-1MA3B cluster (for cars without tech pkg). Had the cluster reprogrammed for $100 to match the mileage of the cluster it replaced.
Here's the before picture, hard to tell it's missing if you don't know it's supposed to be there, but there's no adaptive cruise control information anywhere on the display:
And here's the cluster now, properly showing adaptive cruise / DCA info in the top 40% of the display:
As a bonus, the driver assistance settings screen finally works now (before, I couldn't even access this screen, just like the OP from way back in 2016):
And as a further bonus, the green indicator lights in the cluster for Lane Departure / Blind Spot actually light up now.
If anyone else runs into this problem (say, from another botched Canadian import of an M with tech pkg), here are two places that will sell you used clusters, with 90 day warranty, programmed to the proper mileage:
Tanin Auto Electronics (great folks to work with, but I ultimately didn't buy from them because they couldn't get the part in the timeframe I needed it)
eBay seller instrumentclusterstore (where I got my used cluster - they reprogrammed it to the proper mileage before shipping for an extra fee)
Also, to address a parallel question from this thread, I confirmed via the local Infiniti dealer that they have no tools onsite to change the mileage of an odometer. If a customer needs a replacement instrument cluster, they order the part (which comes in with zero miles), then send the part offsite to a specialty shop to be reprogrammed. For Infiniti clusters at least, used odometers and new odometers are reprogrammed the same way, and there's no restrictions on which "direction" a cluster can be programmed. For example, you could get a used odometer with 150,000 miles and have it reprogrammed to 63,000 miles, and it's the same programming process to take a new cluster from 0 miles to 63,000 miles. I have not seen the programming process firsthand, but having a computer engineering background, I believe they are simply accessing the EEPROM chip directly on the circuit board and adjusting the stored mileage value.
Glad to finally put this oddity to bed!