I've been reading the PxMatrix library source code. It doesn't seem to be using any bit plane based display algorithm. If I've read the code correctly, the ESP8266 makes 8 SPI transfer of pixel row data to create the illusions of a palette of 512 colours. Whereas the Adafruit RGBMatrix library shifts in 4 bit planes at differently spaced intervals to give the illusion of 4096 colours.

I think if the ESP8266 can instead use a bitplane technique, the number of SPI transfers can be cut in half and free up microcontroller compute time to do other things like respond to WiFi, run a simple physics simulation, or process user inputs in a game.