What makes Boro Park and Flatbush two different kehillos, anymore than 13th Avenue and 18th Avenue would be two different kehillos? Why can’t a “Flatbush” Rov have a say in a “Boro Park matter” any less than a 13th Avenue Rov can have in a “18th Avenue matter”?
It’s pretty close to 3 million. What’s the difference if it is 2.8 million or 2.6 million? And furthermore, why are you limiting it to “Brooklyn’s” population? Brooklyn is physically connected to, and part of the same municipal city, as Queens. Which itself has over 2 million. Why are you separating out Brooklyn? If you’re doing that, why not already separate “Boro Park” into its own city for the purpose of counting population for eruv purposes?