Seems Ploytec developed a succesor of the old GM5.
It's USB 3.0 with up to 16x16 MIDI In/Out.
It's not atmel based like the old GM5, instead it will use Texas Instruments TUSB9261.
I called them some minutes before and the friendly Ploytec employee told me, that within the next half year there will also become a board available with pinheaders for the shiftregisters etc.
He gave me the approval to repost the PDFs here.
usb3_midijunction_sch_16x16.pdf
usb3_midijunction_sch_8x8.pdf
usb3_midijunction_sch_1x1.pdf