I would suggest that if you want to try using a different processor, just make a new main board and keep the other V12 boards.? The MPU used on the Teensy is either a BGA or a very dense QFTP, not for the faint of heart to solder, so this one would HAVE to be outsourced to a board house, at least for any BGA like parts and leave the chip resistors, inductors, and caps for the builders to play with.? It might be a sneaky idea to make a clone of the Teensy4.1, leaving out the extra i/o pads, the ethernet stuff, and the boot processor, and add an SWD port. Heck, if someone does the CAD work for this, I wouldn't be surprised if SpartFun might pick it up.
As long as we are programming in C/C++ it should be possible to port any graphic libraries, unless they make use of processor specific blobs written in assembler.? I'd suggest using eclipse and a JLINK mini for the debugger via SWD.? The JLink supports almost every ARM Cortex family MPU, and the mini isn't any more expensive than a good AVR/PIC programmer from Microchip / Atmel. It might take a bit to wrap you head around GDB, but it's a good tool.
The new RP2350 (Pico2) has DSP instructions and can probably be pushed to 200mhz or more.? The "B" version has more pins in a larger package.? Versions with flash "on chip" are coming.? The packages are hand solderable (with a stencil and hot air) it's almost duck soup, I've done one myself.
