I think your upper bound is too many droves, the limit is total Disney Plus subscribers.

Here is some potentially useful data: statista.com/…/disney-plus-number-of-subscribers-…

To me it looks like their numbers may be trending down already so a boycott could be extra effective. If they have lots of customers already considering leaving then giving them an excuse like participating in a boycott in defense of free speech could help accelerate that trend and make a bigger impact.