This project is based on BCM using timer to control OE signal similar to manner used in RPI library? Meaning that if you misconfigure it you get a slight brightness reduction. You are forced to use a min refresh in order to support stable multiplexing operation.
I noticed that you support FlexIO now for Teensy 4. Any plans to support PWM/MM LED drivers? This would make this a snap. By my estimates you may be able to drive 4/8 64x128 panels, but that is really rough.
Another option is supporting S-PWM using FlexIO, granted this is a little weird with BCM. However should be possible. This would increase the refresh rate potentially, however makes configuration very complex. RPI in theory has limits to how far it can do this. Any plans to do something like this?
There is only a few platforms with parallel shifters inside.