Realizing it's a bit too late in the year for it, but how about a Maibock? It's a style that NB does not currently offer and may have more universal appeal than a sour for marketability. No offense to the sour fans, I love sampling them everywhere I go, but I doubt I would ever brew 5 gallons of one at a time unless I got into a nice blending project like the Flanders Pietro was kind enough to share on a bottle swap which was friggin amazing.
My vote for an ale would be an Old Ale or a Scotch Ale as several posts in this thread seem to be preferring to keep away from another IPA or PA.
As a side note, for Pittsburgh Craft beer week this year, they brewed up several collaboration brews for the week and one of them done by 4 Pittsburgh breweries is a White Stout, which I'm fascinated enough by that I'm going to track it down at some point this week to try it.