I figured it was already in development SOMEwhere, in SOME fashion...
"Putting a front end on it to fool it into thinking an ODB I is an ODB II
could be done but not likely since the market is so small."
True. But I didn't really have in mind marketing of such configured hardware - rather gleaning input on an idea. Constructive criticism, you might call it. Some wouldn't have any interest, of course.
Where to mount the projector? Don't have a clue (don't even have my car right now - it's still in Raleigh

, gettin' the tranny swap).
Where is it mounted in later model vettes?
Which HUD unit? How many are there?
What to display? Whatever data is displayed in FreeScan / DataMaster / EFILive / etc. ...
Seems that the advantage of HUD would be integration of display, instead of a laptop, or even a mounted [smaller] smart device...
Navigating the display, in the absence of a keypad ...