In my experience, implementing high-speed low latency comms protocols is not that easy. It's the kind of thing I do at work :) Someone has to write the firmware, test it, support it. Users will also need a way to program boards. I did offer to design and build a board with a micro if someone wants to go that route, but no takers :) In fact, you probably don't need to design new hardware, I think there are already printer controllers with ARM and SPI/I2C interfaces.
I think the only people to have tried the slave processor recently are RepRapPro with the colour Mendel, you might have more knowledge of that than I do. From the little I have gleaned, there were problems with it, which may be partly why RRP took a different approach with Duet.
I think the only people to have tried the slave processor recently are RepRapPro with the colour Mendel, you might have more knowledge of that than I do. From the little I have gleaned, there were problems with it, which may be partly why RRP took a different approach with Duet.