Unfortunately there are no plans to port PPJoy to another platform. As it is PPJoy soaks up a lot of my spare time.
Writing a Linux driver for the LPTswitch interface should be quite simple - perhaps someone can mail the guy who write most of the Linux joystick drivers...
MSDOS is another beast altogether. I don't if you will be able to write a successful driver since most applications directly access the hardware. It is probably possible to include a special driver as part of the DOS MAME executable.
For those of you worried about ghosting - try building a small matrix - the first two buttons of row 1 and the first button of row 2. Try pressing button (1,2) and (2,1) - button (1,1) should not read pressed [Ghosting] Pressing all three buttons should be a good test for blocking.
Of course, if there is anyone out there (and I know you are there

), it is quite simple to design a 208 input interface using a 4-to-16 demux chip.
Glad you guys like PPJoy!