At the moment this allows access to internal ports "miniUART and firstPL011". Could you add support for USB serial ports e.g. Prolific and FTDI please? These install as /dev/ttyUSB0 or /dev/ttyACM0 for the first port added.
My particular use case is USB GPS dongles which, at 10 Euro or thereabouts, are the cheapest way to add GPS to a Pi.