You can do something similar with AutoHotKey on Windows, though I don't have a config for it.
Very likely from Steve Losh (I did this too, and it helped a lot): http://stevelosh.com/blog/2012/10/a-modern-space-cadet/#shif....
For me, when recently trying to remap the left-shift key I found out that it was not a problem for the supposed best practice of using it for C-g/x/c etc, but that instead I had been using a worse practice for typing ":" or """ when the wrong characters turned up al over the place.
Anyway, I suppose the left option key would be pretty good to map to control for emacs, since it's rarely more needed than the right option key.
You have no idea what I am doing with the esc, capslock, and control keys on the left side of my keyboard, but none of them are default.
On the right however I'm just trying to make sure I get a forward delete somewhere. In fact using Karabiner or Seil, the right shift is now shift if pressed as a modifier, but forward delete if pressed alone.