I'm using a planck ez, but the layout is heavily custom:

http://www.keyboard-layout-editor.com/#/gists/eb0696806831fc...

That layout is a bit outdated, i moved super to the outer corner so I can palm press±hold it to manipulate windows in i3 with hjkl. Palm+tap is still enter.

The left hand uses fdsa to move the mouse and vcxz to send mouse scroll wheel events--so it's mirrored hjkl action.

I've done away with the number row in favor of a 10 key, and then mapped the symbols to their finger on the opposite hand, so '@' still goes with 2, but in a different kind of way.

Any symbol with a mate ()[]{} is similarly mirrored (index fingers do these). The idea is that if I ever hurt a hand (which is likely, since I'm a rock climber) I can map a foot pedal to activate a "switch sides" macro and I'll be able to exploit the symmetry to learn to do without whichever hand faster. This hypothesis is untested.

I originally designed it to give my right pinky finger a break, so the hands are further apart to give the index fingers more options and enter is a right palm-press.

Another nice thing about warping your mind to fit inside a tiny keyboard is that you can easily "embed" those neural mappings to a larger keyboard. I have an ergodox ez as well--which has plenty of keys, but I've just ported my planck layout inside of the ergodox and I really just ignore the other keys. I still like it because I can tent either side at different angles, which you can't do with the planck.

http://imgur.com/a/j3dik8b

Disclaimer: this is not a hobby for those unwilling to burn a lot of time tinkering. Also, "maybe it's a bug in my keyboard firmware" is a new and unwelcome thought that must be made peace with. But it's fun for me, and pinky doesn't hurt anymore, so that's something.

This sort of thing works on any QMK keyboard.

I do that with xmodmap under Linux (remapping that useless CapsLock key into yet another modifier key. So capsLock+jkl; are my arrows for years, capsLock+space is my return key, etc). But I would love to have a keyboard that is directly programmable so I can plug it in any OS and enjoy my re mappings without tricky configuration. Is QMK doing such a thing?

Not the parent, but that's the default place for the arrow keys on my Keyboardio Model 01. In Vim I can use them as-is, but on the Fn layer they're arrow keys. The wsad cluster under Fn are mouse pointer keys.

In fact I only have two complaints about the default layout, both pretty minor. One is that {}[]\| are on the Fn layer which took some adjustment for programming. The other is that with alt and space side by side, I sometimes hit alt+space which on macOS becomes some non-ASCII space character that looks just like ASCII space. A find and replace for that works wonders.

you can do with simple cheap Anne Pro 2