Seems like a waste of time. Again, if I was going with this, I'd probably do it the other way around (you know, like every company that made a five speed bicycle did back in the day). Another thing you could do is find a kick back hub and eliminate derailers completely. You'd have two gears, and built into a set of light alloy rims, you could probably make some serious tracks with it. Not sure about cog interchangeability though.