> However, it isn't unreasonable to see a situation in
  > which follower counts on sites like Github, Dribbble,
  > Quora, etc. do become scalable ways of signaling. They
  > aren't perfect indicators of ability or knowledge but
  > then again, neither are college degrees

"Karma"-based mechanisms favor a very specific personality profile. One that doesn't necessarily correlate with aptitude.

Just have a look at the SO superstars -- none of them are auto-hires for all situations. You'd need to evaluate them individually and carefully. Presumably to a degree that makes their community rating superfluous.