I like to approach guitar like subtractive synthesis. That is, you start out with a harmonically rich base signal,and carve/filter away what you don't need/want. Sometimes, the 'carved-away' tone is identical to a humbucker, sometimes to some other category of pickup. But I also like to stumble onto distinctive tones, falling into the 'none of the above' category.
There are probably more varieties of what counts as single coil than what counts as HB. Obviously there is a near infinite set of wire-gauge, #turns, magnet type, base material, and cover possibilities for HBs, but they are often visually indistinguishable. Form-factor-wise, though, single coil designs are all over the map.
All of that said, the slender profile of many single-coil designs allows them to fit, or be moved, into positions where interesting and "different" sounds can be obtained. Consider the pickup on the "John Lennon" Gibson J160 acoustic, that has a very narrow SC pickup at the end of the fingerboard, between fingerboard and soundhole.