65,000 would be a decent chunk of people though in it's own right - *in the current market*. Honestly I do't think billions of people have been shooting slide film for atleast the last 20 years. Think about how many people we have on the planet, how many of those actually use a camera, and how many went past color negative, or even did anything with said camera more than once a year.
We'll never get real figures, sadly.
I still shoot E-6 though, I've purchased multiple quantities of 135, 120, and 4x5 from Freestyle in the near past as well. Unfortunately I just cannot afford 8x10, nor do I shoot it in any emulsion (and this saddens me, because it means I'll never be able to see an 8x10 transparency of my own).
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.