After a few idle weeks, I finally decided to order the current rev1 of the TMC2130 board design. I found this web site (pcbshopper.com) which compares the price of various PCB manufacturers and matches them with your board specifications.
As luck would have it, a day after I sent the files to the board manufacturer (jlcpcb for the rev1), I had an idea of adding thermocouple interface.
Here is the rev2 of the board with dual thermocouple connectors. It should work with MAX31856, MAX31855 as well as the good old MAX6675 chips. All of these are based on some form of SPI interface, and I just added them to the bus.
Because I used all I/O pins, if you decide you need thermocouples, you’ll have to sacrifice the two controllable extruder cooling fans. Most 3d printers come with “always on” cooling fans anyway.
The thermocouple connectors use generic SPI(MISO, MOSI, SCK, CS) + 5V power and GND pins. In theory one could connect other things, with appropriate software patch.