There were many professional applications for LD players. Flight simulators, video encyclopedias, museum displays.
One popular application was using every frame of a CAV disc to store still images instead of video. These would be pictures of flowers or insects or whatever. Since a single side of a CAV LD can store 54,000 totally discrete frames you end up with a pretty compact method of storing images by the standards of...1987, or whoever this was. These things would often come with a huge book with an index of all the images in it and barcodes under the descriptions. A special barcode reader pen/remote thing was used to instantly access any image.
The serial port can be used to control all LD functions via computer. This would allow you to make something like a museum display with huge child sized buttons or semi-interactive games. This is how Dragon's Lair arcade machines work. As long as you don't need overlays you could basically make a shitty Cliffhanger game out of anything you had on LD. According to Wikipedia, this is exactly what someone did,
"The floppy disks included some sample programs created with the editor for use with the first five LaserDiscs in the Tenchi Muyo! anime series."
Since I own all five of those LDs I can tell you that you'd have to be pretty clever to pull off anything fun with them but...I would like to see it some day. Presumably since this is a Laseractive PAC you could also make overlays like...score counters or something? Hard to say.
Like I said, this serial port is built into almost any Pioneer player with a "V" in the model number. These players will also have dip switches on the back that enable endless repeat and other functions. They tend to be mad cheap and they are built like f*cking TANKS so they pretty much always work. Most predate the existence of Digital Sound tracks so they don't make great main players.
