On reprapro.com there is a blog post regarding multimaterial printing through the same hotend using a railway concept. Apparently this was attempted by one of his customers and I've seen reprappers here try similar things .

I am currently working on building a coreXY Mondrian Variant with a bowden system and want to incorporate 4 color/ material printing. I have been looking at the Kraken from E3D online or simply using 4 reprapro or even 4 E3Dv6 hotends (They all total to around the same price). This could reduce my moving weight even further while simplifying the electronics.

After seeing this concept I am curious to see if anyone has any experience implementing it or a similar system:

What material(s) did you print?
Did you combine different materials using this concept?
Did it hold up well after multiple retractions during a longer print with multiple color changes?
Were there any issues with jamming due to stringy filament?
Were there any retraction issues?
What GCode did you use for tool (color) changes?

To my understanding there could be issues with pieces of filament getting stuck during retraction or the swollen part of the filament preventing retraction if it is attempted after cooling. However, if you are printing with lets say 4 different colors of PLA which require similar printing temperatures then couldn't the remaining bits be extruded during a purging step?

I anticipate problems when combining different materials but if something like this would allow be to print multiple colors of PLA or simply one color of ABS, nylon, or other materials through a single hotend I would be interested in trying such a setup.

Any input would be appreciated.