I'm going to pile onto the wagon of those not in favor of this. I only get to go to a couple of conventions a year, and I've chosen BronyCon because it is geared directly to what I love. I can handle a little crossover if it's pony themed, but pure non-pony stuff is not what I spend so much money for.
Last year's attendance was noticeably smaller, and someone said 24%. Having it the weekend after July 4th may have been the biggest issue there, but I expect this year will be more of the same. Having it the same weekend as Otakon(at least that's what someone said) is just asking for a huge attendance drop.
As much as I would love being a stalwart, it's just too expensive for me to continue going if the convention veers away from being pony-focused. Other fandoms simply do not like us. I know because I'm in other fandoms and get heat because I have ponies on my stuff. I fear seeing BC overrun with fans that don't like what we love.
I don't want to see BC die, and the very thought depresses me. However, I'd rather see it simply stop than be absorbed by another fandom.