As for the beer itself, I do find this style really interesting. When I brew mine I brew it from the ground up with dark malt and I use slightly different hops that are a bit more earthy and dank to better go with the character that the Carafa Special adds. A lot of people will say that Carafa Special only adds color and no flavor but this simply isn't true. It doesn't add much ROASTY flavor, but it does add a whole other dimension to the beer - to me it's akin to a dark fruit character, like plums. I really feel like it's more than the sum of it's parts - it's not just an American IPA with a dark color.
Also, it's a crowd pleaser. I recently took six different homebrews to two different tasting events at two different brewpubs and in both cases the "Black IPA" was chosen as the beer they'd like to see brewed there as part of the regular lineup. I've spoken to quite a few people about it, both seasoned beer drinkers and casual beer drinkers and many of them agree that this beer bridges the gap between the purely stout-drinking crowd and the purely IPA-drinking crowd. Both teams can usually find something they like about this beer. It helps expand some people's horizons and get them more accustomed to flavors they otherwise wouldn't have thought they'd like.
Another effect this may have is helping to balance out competition entry numbers in certain styles. IPA typically has the most entries in many competitions. Perhaps with a Black IPA category more people will enter this instead of the IPA cat and things will be a little better balanced. Assuming that is a good thing
I agree that it is kind of a gimmick. "Hey we're bored with IPAs, let's just make em BLACK!" But regardless of where the idea may have sprouted, I do think there's some merit in this "style", even if it's just for fun. But I've had a lot of success locally with this beer and find that people who normally don't like hops find themselves intrigued with this beer and before they know it they've drunk the whole pint. If this style can help more people appreciate a wider variety of styles then I'm all for it. But if it really is just a gimmick that doesn't serve any real purpose then I'm sure it will come and go like a bump on the road. For now though, I'm having fun with it. I'm interested to see what the character difference will be between Carafa Special and Chocolate Wheat, or Chocolate Rye, being that all of these malts have no husk.
Cheers



