IMPORTANT NOTE: This will not work on a Prusa i3 or really anything that is complete and available. I think the design is pretty cool, but you'd need to build a machine around it.
This is combined carriage and extruder for 70mm spaced vertical x-axis. It uses 4 lm8uu bearings and can be removed from the machine without tools or disassembly of the x-axis. With the idler open the hobbed bolt and gear can be removed and cleaned without tools. I've done an extruder test and it rides nicely on the rails, but i wont be able to print anything with it until i build the rest of the machine.
X-ends available here:
Print. I've printed this in ABS with some warping, PLA might be better.
I recomend infill of 50% or higher. The extruder itself is very similar to other wade designs. Except the drive bolt, all hardware is M3.