Yay - i like the idea and Polar looks pretty cool. Like Delta … Also we could upscale this to room size i think ^^
http://hackaday.io/project/812-Theta-Printer
Mmm… plastic covered chocolate colored with markers, yum 
The thing about both polar and delta machines is that the positional resolution varies from high near the center to lower at the outer edge. There’s a lot of discussion about Moire patterns on deltas here. Not that they are detrimental to print quality. If you have high resolution motors controlling the build platform of a polar machine you should be able to get acceptable positional resolution across the entire build plate.
Interesting idea, but without specialized slicing software, it seems unlikely that both extruders would be able to work simultaneously.
The two extruders must have enough travel to collide unless you only want to create parts with a hole in the middle. The firmware and slicer could prevent collisions but the tip of each extruder must reach the center of the bed.
I imagine you’d only want a single extruder in the build area at a time and would just swap out with material changes within a given layer
its a pretty damn cool design no matter what you say. What is the crunching noise in the video though? Is it the gt2 gears and teeth messing?