Here is another project idea I never really started working on: A computer keyboard that has a small LCD in each key cap. I'm convinced that there are legitimate use cases. After all, the function of the keys changes according to context. Different applications have different shortcuts, when I press and hold the Ctrl or Super key, the whole layout practically changes. Most people don't remember useful keyboard shortcuts, if they try to memorise them in the first place (if the learn about them to begin with). It would be nice to have the markings on the keys reflect their role. In some special applications, like video editing, a completely custom keyboard layout would be useful (a cheap alternative to buing a custom video editing interface input device). In computer games, only the useful keys could light up, as well as display what they do (which depends not only on the game, your custom layout, the current situation in the game, as well as what happened earlier in the game, e.g. what items you have in your pockets). You might want to write in different languages and need different keyboard layouts at different times. You could have icons or descriptions of key functions be displayed whenever you hold a modifying key, to see which shortcuts are available. You could have a second keyboard with an additional layout to give you access to frequently used functions, and have the keys display the relative application icons or describe what they do. And it would just look cool.
The idea has been in my head for years. I even board the electronics to build a few keys to try it out. But I never build one because I think it would have been too much work on the side to get it done well, considered I come by very well without one. Now I learned that somebody else has built a keyboard very similar to what I had/have in mind. To be honest, I never really get very deep into the keyboard building community to know whether a keyboard like this already existed. I think when I had the idea I didn't even know how big the mechanical keyboard fan community is and that DIY builds are such a big thing.
The project I stumbled over is the Poly Keyboard by thpoll. Here is an article about it in the Keyboard Builder's Digest, here is the Github repo. Apparently (according too the article) it isn't the first of its kind. But it's the only one I've seen.