Extruder Feedback

I was just thinking about FDM extruders and how mine occasionally strips out the filament. When it happens, the usual set of words are uttered and I go and cancel the print. It would be nice to have a quadrature encoder attached to the idler wheel. But when a strip occurs, the idler wheel just flaps around in the breeze, and will probably not give a decent speed to feedback for feedrates if and when I upgrade to a stepper motor extruder. So I got to thinking about different ways of ensuring the feedrate is properly measured.
At first I thought that it would be neat to paint stripes on the filament as it was fed into the extruder. After the extruder gear there would be an optical sensor that would detect stripe/not stripe. It would be a mess and add another consumable, not to mention making speckled prints if a visible ink or paint was used.
Then I thought: “Wait! The extruder is already marking the filament!” Just place another extruder gear below the extruder such that it is turned by the filament. Attach a rotary encoder to this gear, and then firmware will be able to detect if a strip has occurred and how fast the filament is being fed. What do you think?