The Mark XII keyboard is as yet unbuilt. I'm happy enough with the Mark XI physical design. With a little bit more work, it's manufacturable, except for the electronics. For that, I need something which consumes less power, is smaller, can implement chording, and implements the HID profile. That perfectly describes the Broadcom BCM2042 bluetooth keyboard controller.
Unfortunately, that chip is a BGA chip, which is hard to work with. Fortunately, several companies implement Broadcom's 92042 bluetooth keyboard module. Blue Packet is one of them. They sell the 2042 on their BP20422 bluetooth keyboard module (to which I can't link directly, but it's off the drop box.) They haven't (yet) committed to modifying 8051 firmware with the necessary chording algorithm, but I'm confident that I can talk them into it. Talk, yes, and money. Unfortunately, the module on the PC board isn't working. I suspect that I toasted it while soldering it to the PC board.
Speaking of the PC board, my friend DJ Delorie very graciously answered my questions about how to use PCB, the Open Source PCB package. Then, he even volunteered to make the board for me. Ahhh, it's to nice to have college buddies. They make your life so much easier. This first cut at a board is just a footprint adapter. I wanted something from which to hang discretes, as well as have good access to the pins. Plus, Blue Packet hadn't yet sent me the schematics.
I have ordered another ten modules from Blue Packet. That should be enough to get a good prototype working, even without the chording firmware. I'll only be able to type 7 keys without chording, but I'll have all the electronics in order at that point.