I "made" one - and contributed upstream to the firmware as well! Running and testing on a Replicator 2X, you'll see I've built my own firmware. Upstreaming my changes as I make and test them!
I can print pretty fast (non-travel moves speed limit at 100mm/s) using Cura now... next step is to try Octoprint.
If only my "upgraded extruder" wasn't slipping so much...