I will be implementing similar by an arduino uno via serial2 pins 18/19 or i2c, most likely uno in i2c slave mode.
The uno will control 3d printed heads on nema17 stepper motors.
How about just general I2C stepper control, as this can be used multiple ways, such as protein skimmer cleaner, fish feeder, stirrer of all types.
I was going to do all this by connecting an arduino via serial bytes on pins 18/19 or over i2c on pins 20/21, or donating the pins used for PCF8575 and sending pulses and converting them to step counts within the uno.
Numerous ways to do it, you need to decide how to make the interface
I do not think you should concentrate on zeolite alone, instead, general stepper control. Everything will be "which motor" "what time" and "how many rotations" in all instances, so better just to go strait to stepper control, instead of zeolite specific..
People will just change zeolite to something else!
i2c stepper motor drivers look very nice, I did not know of them until I read this post!