Reading old literature and journals, i've found out that there was some form of HP42sx prototype actaully present and publicly used by a Corvallis engineer. The I/O functionality had been burned to a larger ROM and a hole cut in the case to take the hand wired socket. But it worked, and was there!
A fully disassambled ROM image from a 42S would make building an IO/extended functions ROM this much easier. I'd also vote for strictly Infrared IO due to power and space.
A disassembled 17Bii ROM would also add the ability to get the code for some of the financial and statistics functionality into a second ROM.
I'm sure that it would be easy to get submissions sifficient to fill any ROM package that was made. (to preserve the 'pioneer-ness' of the calc, it would have ot be a small surface mount item.
Periodically, steps are taken by various people to try and get closer to this Holy Grail of Pioneer calcs.
So here I am, starting the next cycle :)
Maybe I can get a disassembler running on a 48 to handle this.
and- for anyone building an emulator, go for it! a good 42 emulator would make final builds of a ROM much easier