At about the 26 minute mark of volume 17, they say that they're developing an adapter to allow the PC-FX's CD-ROM drive to be used by the PC-x8 line of computers (also made by NEC and ubiquitous in Japan in the early 90's). This never surfaced, right?
They also say they're developing a board to allow PC-FX games to be played on the computers, too, which they did follow through on (PC-FXGA).
Finally, they vaguely suggest that they're developing add-ons to turn the PC-FX into a multipurpose home electronics hub, including a fax receiver and various components to turn it a "computer terminal".
"There are so many possibilities for the PC-FX, we can't possibly introduce them all!"