I'd kind of considered printing a rather small thing (seriously, 3x3x3 cm or so) in grey using this technique (using white and black filament). It told me it'd require 140 (== number of layers) filament changes and it'd take 5 hours. (In fairness, if I wanted to print 10 at once it'd probably take a similar time.)

So... honestly it's kinda silly IMO. If I wanted to mix colors in a hacky way I'd just... wait, hold my beer.