I totally agree. There is more than enough "unmapped" area on the motor & sensory homuncului[1] (creepy image warning) to be repurposed as an I/O channel by retraining the brain. In general, brains are plastic enough to remap senses like this[2] given a handful of months' work/practice. Adults are capable of learning ASL, for example, which uses completely different "output channels" from spoken language. Even when learning to drive, the car can start to feel like an extension of one's self (and I'm not a car person at all). Famously, people who become blind begin to develop better acuity in their other senses because of all the "freed up space" in the visual cortex (which I'm sure is an oversimplification, I'm not a neuroscientist).

We have so much raw data coming into our brains--via sight and sound especially, but surprising amounts via other senses as well--that I see little reason to add "additional senses" or outputs when we have rather high bandwidth already. Heck, my thoughts run ahead of my speech or typing fairly often, and both of those are pretty low-bandwidth channels.

One-hand chorded keyboards[3] are perennially reinvented by someone with an Arduino and a few buttons (not to belittle that work!) but you can't just pick up a chorded keyboard and type as fast as a regular one, so they are generally treated as a novelty. But if one spent as much time learning to use a chorded keyboard as they did a regular one, I'd bet they'd be just as fast. Perhaps the reason fluent computer users show little desire for better human-computer interfaces is that they are afflicted by a generalized form of baby duck syndrome[4]. To mix metaphors in a really confusing way, interacting with a computer with a keyboard, mouse, and monitor feels like using GNU nano: shallow learning curve, but it tapers off quickly. I wish I knew the Vim of HCI: I'd be willing to practice for years to adapt to it, to compute more efficiently for the rest of my life.

[1]: https://en.wikipedia.org/wiki/Cortical_homunculus [2]: https://en.wikipedia.org/wiki/Cortical_remapping#Plasticity [3]: https://www.stavros.io/posts/keyyyyyyyys/ [4]: https://en.wikipedia.org/wiki/Imprinting_(psychology)#Baby_d...