A 3-dimensional keyboard design

[wolfv]

Here is an interesting paper from the Graduate School of Science and Engineering, Waseda University, Tokyo, Japan, 2016:

A method for using one finger to press three separate keys on a three-dimensional keyboard
https://robomechjournal.springeropen.com/articles/10.1186/s40648-015-0039-6

[iso]

Looks like you'd be limited to 3 "rows", also, other hardware limitations, switches soft enough to not mess up your joints on the long run and small enough to be implemented to work with such design

[Mandan]

The upper row would have to be adjustable somehow, so people with smaller hands could press a switche on the bottom row without pressing the top one too.

[jacobolus]

The high key looks pretty ick, but the other two are good. For a third key, the best is to locate the top roughly where the fingertip is in the first image.

For a practical implementation of this idea (that never quite made it as as commercial product), see the DataStealth, https://geekhack.org/index.php?topic=55099.0