A DESSERT JOINT/ESTABLISHMENT/EATERY THAT SERVES SEASONALLY APPROPRIATE TREATS ON A PREDICTABLE ROTATION
Perhaps the fact that we don't have a name for a place that serves different desserts but is not a bakery indicates that this truly is a gap in our food service industry. (It's also quite possible I just can't think of the right word, but let's go with this first theory...)
This is my idea: a year-round shop that sells, for example, ice cream in the summer, apple cider doughnuts in the fall, pies and hot chocolate in the winter, and cupcakes in the spring. New England has plenty of ice cream stands. Just keep them open all year round, maybe have a co-op model where the space is rented by the season and every three months a different sweet treat is sold to the same loyal, local customer base. Seems to make more sense than trying to anticipate the next dessert trend or trying to sell a single dessert item year round.