So I asked about this in the PJRC forums, and evidently Paul has made a board available from OSHPark here:
https://www.oshpark.com/shared_projects/d3J03Zeb

Their bootloader chips are available here:
https://www.pjrc.com/store/ic_mkl02.html

It's still missing the bill of materials and requires surface mount soldering to put it together. I'd have to know the cost of the other parts to determine whether it is economically better to build this or to buy a Teensy 3.2 and drop it on my board.
Let's take a guess.
The bootloader is $7 and the processor is available on Mouser for about the same price. The crystal is somewhere between $0.50 and $1. $1.50 for the USB connector. I'm going to guess $5 for the rest of the parts. So you can probably build this for maybe $21? It has a few pins that might be strange for Teensy shields, A10 and 11 where AREF and GND were before, but at least the audio shield seems like it won't mind that.

Mine is going to be $8 + $20 for a Teensy, so definitely more expensive, but it might be a little easier to assemble. (If I was going to sell them, I'd have to charge more... so it is already a loss as a product...)

Given that they have a reference board design available, I imagine the the official assembled boards will be on their way very soon.
Hmmm. Should I even bother to build mine?