Would it be possible to implement a feature, in the future, to assign individual buttons via the H90, so as to allow for more third-party pedals to work with the H90?
Not sure what you mean by this, but right now, the H90 can detect which switch is being pressed. If you enter System Settings and go to I/O, on the third page we can find the I/O-Exp & Aux settings. Under Pedal 1 and Pedal 2, we can assign whether it accepts switches or an expression pedal. If we’ve chosen switches, we can then use the third Quick Knob to enter Calibration. As you press the switches on your 3-button aux switch, the H90 will tell us what switch number each press corresponds to. Once we know this, we can assign any switch to any parameter or global settings.
It does not matter how your chosen aux switch is wired internally. The H90 accepts all of them. The only aux switches not compatible with the H90 are those wired with internal resistors like the Strymon MultiSwitch.