i just happen to have one, new in box! i bought this years ago at Weird Stuff Warehouse when they were still around. i have no idea why, but i'm glad i did.
looks like it is essentially the same protocol as the version of the mouse (type 4?) designed for the SPARCstation. the output is open collector, inverted async serial, 5 byte.
time to build an adapter. the connector is RJ11 (technically 6P4C) but it has these pins sticking out, presumably so you can't plug it into a phone jack.
@tubetime You only need the RGB if your display does sync-on-green. This is why I have a bunch of NEC LCD1990SX, they do sync-on-green and support a 1:1 aspect ratio in addition to stretching to fill the screen.