I just put in a pull request for adding 3-state sticky key layer function support that functions like sticky keys for modifiers (shift, ctrl, alt, command) in Windows or OS X where you can key in chords by pressing modifiers then alpha-numeric keys sequentially rather than simultaneously. When only keying a single key on a layer, you don't have to pop the layer afterwards, the pop is automatic. If you press the layer sticky key twice, it locks the layer and pressing it a third time to unlocks it.
In my current layout (colemak-jc-mod.c), I have sticky layer keys on the inner most keys on the bottom row, used as thumb switches. These keys toggle a symbol layer which is indispensable for programming. I also have my lower, inner layer keys as sticky layer keys for a numpad/function key layer, though I find I'm more often using the left-hand middle thumb key to do a standard push/pop on this layer for multi-digit numbers and repeated function keys (F6, F7, F8 for debugging).
As with normal layers, you can use kbfun_layer_pop_all() to go back to layer 0 if you get lost.
Here's my fork if anyone is interested:
https://github.com/judascleric/ergodox-firmwareUse "make LAYOUT=colemak-jc-mod" if you want to build with my layout, which is almost this layout
https://www.massdrop.com/ext/ergodox/?referer=EAZJPJ&hash=f8c739b3dbfb1d01500db57fbe1bcefb (minus sticky toggles and manual assignment of kbfun_shift_press_release() to most of the symbol layer).
