Earlier this year we designed a custom PC104 board using the NXP RT1062 ARM processor (same one as on the Teensy 4.x). This is the new hot kid on the block, running at 600 MHz.
Our BASIC is now much more easily ported into the native development tools (in this case MCUxpresso), and we have it working well enough to do some benchmarking.
Will the RT1062 BASIC become a product, it depends on user interest.
The PC104 board supports 8 serial lines, and has expansion for USB, SDcard, buffered ins/outs, AD. Most all pins of the BGA are brought out to headers for further customization.
How fast is this, well three to four times faster than our previous ARM Cortex leader. Details here