While I'm not sure if this video of the 1995 New Paradigms for Using Computers workshop actually shows a dual-nippled Thinkpad, it does include a great talk by Doug Engelbart, and quite a few other interesting people!
https://www.youtube.com/watch?v=oD9NUWDCyHI
The multi-Trackpoint keyboard was extremely approachable and attractive, and everybody who saw them instantly wanted to get their hands on them and try them out! (But you had to keep them away from babies.) He made a lot of different prototypes over time, but unfortunately IBM never shipped a Thinkpad with two nipples.
That was because OS/2 (and every other contemporary operating system and window system and application) had no idea how to handle two cursors at the same time, so it would have required rewriting all the applications and gui toolkits and window systems from the ground up to support dual trackpoints.
The failure to inherently support multiple cursors by default was one of Doug Engelbart's major disappointments about mainstream non-collaborative user interfaces, because collaboration was the whole point of NLS/Augment, so multiple cursors weren't a feature so much as a symptom.
Bret Victor discussed it in a few words on Doug Engelbart that he wrote on the day of his death:
http://worrydream.com/Engelbart/
>Say you bring up his 1968 demo on YouTube and watch a bit. At one point, the face of a remote collaborator, Bill Paxton, appears on screen, and Engelbart and Paxton have a conversation.
>"Ah!", you say. "That's like Skype!"
>Then, Engelbart and Paxton start simultaneously working with the document on the screen.
>"Ah!", you say. "That's like screen sharing!"
>No. It is not like screen sharing at all.
>If you look closer, you'll notice that there are two individual mouse pointers. Engelbart and Paxton are each controlling their own pointer.
>"Okay," you say, "so they have separate mouse pointers, and when we screen share today, we have to fight over a single pointer. That's a trivial detail; it's still basically the same thing."
>No. It is not the same thing. At all. It misses the intent of the design, and for a research system, the intent matters most.
>Engelbart's vision, from the beginning, was collaborative. His vision was people working together in a shared intellectual space. His entire system was designed around that intent.
>From that perspective, separate pointers weren't a feature so much as a symptom. It was the only design that could have made any sense. It just fell out. The collaborators both have to point at information on the screen, in the same way that they would both point at information on a chalkboard. Obviously they need their own pointers.
>Likewise, for every aspect of Engelbart's system. The entire system was designed around a clear intent.
>Our screen sharing, on the other hand, is a bolted-on hack that doesn't alter the single-user design of our present computers. Our computers are fundamentally designed with a single-user assumption through-and-through, and simply mirroring a display remotely doesn't magically transform them into collaborative environments.
>If you attempt to make sense of Engelbart's design by drawing correspondences to our present-day systems, you will miss the point, because our present-day systems do not embody Engelbart's intent. Engelbart hated our present-day systems.