@Forum-user we've looked into this and the limiting factor is that the MCUs we use on expansion boards only provide a single quadrature decoder. We've looked at using an external circuit in combination with a counter on the chip to provide a second decoder but that wasn't possible to do with sufficient performance.
The MCU we use on the 6HC and 6XD main boards can provide 2 or 3 quadrature decoders, and there may be STM32 processors that can too; so we'll keep this under review.
Another possibility would be to use linear axis encoders that support BISS protocol instead of quadrature.
