Been down one of those roads, but haven't updated the Macintosh Portable Slot Hackage thread. There are two signals on the Portable's PDS that are flies in the ointment IIRC. That's for a straight processor upgrade though, so I didn't look at the slot addressing/memory map aspects of the Portable PDS. I can tell you that there is next to nothing/officially nothing in the power budget for an expansion card however . . .

. . . makes me wonder why they even bothered to put that slot in there.