I would be happy to address your question. As a former shop owner myself, the first consideration is how many machines do you have and how many flavors/products of soft serve can you offer?
When I was running a soft serve dessert yogurt shop, we received all types of requests for different products and different flavors. Some customers wanted a low carb product, one or two customers would want a banana yogurt. “When are you going to run the strawberry cheesecake?” “I need a no sugar added product, what date will you be running it?”
The absolute bottom line that every shop owner has to determine is how many machines do I have and what are the high volume products and flavors that will sustain my business and keep us profitable?
Selling two servings of banana frozen yogurt a week does not justify running the product, in my experience.
It is my experience that you will never be able to please every customer that walks in the door based on their flavor preference, product preference and dietary needs.
You need to determine who the customer base is that you are serving that will continuously come to your shop to enjoy the products you’re serving and be repeat customers.
So, my recommendation is to use your machines wisely to meet the demands of the volume business that you want to obtain.
If you want to try and meet the needs of a customer that does not justify using one of your machines, you can always offer a blender smoothie with their desired request. There still might be some restrictions on this depending on how many requests you receive and what the minimum amount of product is that you need to purchase from your supplier.
So, back to your original question: If you have a customer base that is large enough to justify using a machine to run a vegan soft serve mix, implementing this product could make great business sense. To assist in your decision-making process, you might want to offer a sign-up sheet in your shop for 2-4 weeks to collect names of those customers who would purchase a vegan soft serve.
I hope this gives you some insight into the product selection for your business.
Best to you and your business,