I don't remember if it got released officially or if it is only a prototype, but there was also a personality card referred to as Bordeaux with DVD decoding hardware on it. I believe it was a Wings with additional hardware. I don't know if it had SCSI/IDE on it or if it was just the decompression hardware for MPEG-2 video.
Given that every beige G3 board that ended up being built had three normal PCI slots on it, I don't think Apple meant for the personality card slot to be available for more third party development. They could have used it for their own purposes, especially if (I'd have to go look at my G3 tower, too) the whole thing has its own back-plating, but really, I think the whole idea was to make manufacturing A/V and non-A/V configurations of Power Macintoshes easier. Basically, to avoid the situation Apple was in in some markets, selling the 7300/200 and 7600/200 alongside one another, one with and one without a/v functionality.
Hypothetically Apple could have taken it further and built, say, a video input card that didn't have outputs, for like a video conferencing configuration (like the 7500) but even though the slot was almost certainly technically capable of it, I don't think Apple wanted to over-extend itself too much by building different options.
One side-note, I keep seeing things about the Whisper and the comm slot, but the
Wings also had it - so you can have your dial-up and your A/V too. That may have been mentioned.
As a totally wild hypothetical, if I was giving Apple advice on what to build, an interesting personality card would have been a card to add the blue-and-white G3's USB ports to a beige, and perhaps a 16-meg Rage128, to essentially update a beige G3 to most of what was important for OS X. Not that you can't install a Rage128 and a USB card in a beige, but it would have been an intriguing way to shift one of those machines away from hardware not totally friendly to OS X (the Wings a/v card in particular) to hardware that will work better, and possibly retain some more compatibility with, say, Mac OS X 10.3 and 10.4.