I see the case where someone using shopify could want to do something like this. If enough shopify users ask for it, they could add it, but it's a pretty esoteric feature needed by relatively few shops, because traditionally, individuals shop individually, rather than with a group.

Group buying isn't an unheard of concept. Many buying groups pool their resources to receive discounts on large orders from manufacturers. This could be a feature for such manufacturers to add to their ordering systems.

Still, the hurdle if integration is going to be a big one for you. For example, how do you let syncfu know how many products you still have to sell? How does the store owner coordinate sales such that they don't sell more than have been requested to buy from syncfu? Why would a seller want to sell their goods at a reduced price to the same individuals who are likely to buy it individually anyway? Also, you still have the logistics problem of shipping all those orders from the "group" to the individuals who grouped to get the discount so as a store, your margins decline due to increased overhead for lower sales. Discounts for large orders are usually only possible because there is reduced overhead in shipping and account management.

I think you may have a hard time selling this feature to stores. However, if you create a competitor to shopify that has this as a feature, then all the shopify customers who want to sell this way could be potential customers for you.