Having back end knowledge of commercial brewing ingredient and production costs, I believe the only way to do this profitably is to offer a few base styles and give some customization options on the post fermentation processes/ingredients. To brew individual small batches with complete customization is very expensive and time consuming. The only way I think you would profit off of it is by doing so in a contract brewing capacity and batch sizes of 10 bbl or more for B2B sales and white labeling.
That said, another way to be profitable is not off the brewing process itself, but creating an experience where the customers ultimately hang out and drink your house beers in a tasting room setting while their batch is being brewed. So long as they pay $6-7 per pint, that would be profitable enough to offset the brewing expense of their own batch and cover your overhead and labor. However, strictly custom brew on premise profitability is hard to achieve and the market for it has dwindled in recent years.