I was an early proponent of the idea that Brown IPA was a further redundancy in the 2015 BJCP style guidelines - after all, we had American Brown Ale, American Porter, American Stout, and Black IPA.
Surely, we didn't need Brown IPA, when all four of those other styles are available. To be perfectly frank, I'm still not sure we need the defined style, but I've more than come around to the idea that these are (or, at least, can be) distinct beers. The key difference is that although Brown IPA would fit in any of the aforementioned dark-and-allowed-to-be-hoppy styles, it wouldn't be a very good representation of any of them. To use a favorite analogy of mine, a building needs four walls and a roof - but even though a shack has those, it doesn't make it a good or attractive house.
Brew yourself a couple of Brown IPAs - targeting that style specifically - and you'll soon find that this isn't just an American Brown Ale with a little more alcohol and hops.