I plan on at least hooking the power-on and LED status to my shutdown controller. I have the first revision of the xenarc that doesn't power up when a video signal is detected. The other option is to figure out how to eliminate the latching power-on/off and just make the display power up when 12v is applied. I was planning on at least extending the other switches so I could make adjustments if necessary. I don't really want to put the buttons on the dash though.
I am already very short of serial ports, so I am not sure if I can interface them to the computer. I might use the parallel port to control a few things such as the display.
I might pickup one of the USB<-->24 I/O port boards.
http://www.futurlec.com/USB.shtml
I have several USB<-->RS232 adapters to convert things like my shutdown control, Touchscreen, ODBII, etc. Initially they wouldn't work when more than one was used. I researched the chip (ftdi), and found that they support a serialized EEPROM. On the adapter, the EEPROM was simply missing from the PCB board. I ordered some EEPROM chips from futurelec, soldered them on, and used the OEM chip programming tools on FTDI website. You can program your own USB vendor id, and serial # for each device. Now each adapter is recognized as a unique device and I can install a driver for each and configure a unique COMx port.