[SiriusHardware]

To cope with any likely alphanumeric matrix keyboard I think 8 column + 8 row optos, one lot of 8 with emitters and one lot of 8 with collectors connected to a common interconnecting rail as per the current 4 + 8 of the present Pi-uploader - turn on one of the column optos and one of the row optos to press any single key in a matrix of up to 64 keys, and also at least two undedicated optos to hard-connect across the row / column intersection of CTRL and the row / column intersection of SHIFT so that the interface can press either of these keys by energising a single opto at the same time as it is energising a pair of optos to press any other key. That's still only 18 optos / GPIO pins and the same circuit could still be used, with appropriate GPIO / opto mapping, for the Pi-uploader.

For Triton or other computers expecting 8-bit parallel input from the keyboard just use the 8 row optos or 8 column optos (as appropriate) and one of the undedicated single optos for the strobe.

One interface to rule them all.