My first "job" between school and university was to assemble a bunch of keyboards for banking terminals. They used configurable key caps in that a printed sheet was snapped under a transparent keycap cover. I suppose I must have been working on a short production run for a small bank or a trial project, that didn't merit screen printing the keys.

As I worked through countless of those keyboards I mused that what it needed was a little screen on each keycap, so I could just do my job using software.

This was in 1982. Seems like we're nearly there.

That's actually been done in a few different products, I think the only enduring product though is the StreamDeck.

The most impressive was the Optimus Maximus someone else mentioned in a comment.

[oops, double post]