I have successfully connected the new board to the new Teensy-based #Arduino Desktop, and although I do not have a *valid* signal yet, I do have a signal, and the data exchange is working :-)

Obviously, at this point, I have assembled the PCB.  There was a PCB bug, screwing up the direction of the level translator, but after fixing this I was able to communicate with the RA8875.

Based on the Adafruit RA8875 library (https://github.com/adafruit/Adafruit_RA8875), it seems we can query register 0 and should expect 0x75 to be returned, to confirm proper connection.  Sure enough, this worked exactly.  After this, we can initialize the video registers.  I just used Adafruit's settings for their 480x800 displays. At some point while loading the registers, the attached monitor woke up and told me the signal was invalid - which indicates that I am actually sending at least the sync data over the wire, even if incorrectly!

This all was after connecting the RA8875 IC backwards, of course.  Well, it still worked after I flipped it despite this abuse, so I'm grateful.

The next thing for me to do is write a small library for talking to it, or perhaps a library for #NTIOS. The initialization sequence doesn't look too complex, if anything it will just be difficult to get the right settings.