I didn't know about concord grapes for a loooong time. To me, grapes were green or red (no black!), and a world away from Welch's, which, though it claimed to be juice, couldn't possibly have been.
Concord grapes have been, for me, something from the east coast, something I've only experienced in adulthood, and something that I still, each year, can't really believe. Their intensity and sweetness is almost too much for me, making my tongue twist.
That's why concord grape sorbet sounds perfect—a concord grape with it's edge cut by cold. Much the way Welch's only tasted right over crushed ice. I link to the Gourmet version of the recipe because the news of the magazine's demise was just released today. However, on Epicurious, in the comments, there are two perks. 1) Using agave instead of sugar. 2) If you don't have an ice cream maker, and, like me, the one you borrowed reeks of old milk and you return it without ever using it, you can freeze the grape mixture and then run it through a food processor to get a good consistency.