Backstory: Crowd buying on a large scale is considered normal across many different industries. Mass drop (now drop) carved out a niche in the computer/electronics space. Scaling down this concept into small groups with smaller thresholds is becoming trendy in non US countries. Zippserv is popular in India for real estate. 

Taking this smaller group concept and applying it to e-commerce could have big potential.

The Idea: Group buying plugin for shopify. 

Deep Dive: You would build a shopify plugin that store owners could add to their store as alternative way for customers to buy their goods. The idea is you would offer an item at a discount if they can bring 4-10 of their friends to the site to buy the same product. The idea is that it would lower cost of acquisition by using the first customer to bring on 3-9 more. 

The plugin would take money from the original purchaser but credit back any discounts after a set period of time for every referral source they brought in. You would limit the time window for the opportunity to create urgency.   

Validation: India has Zippserv, a group buying real estate platform. There's a larger scale crowd funding app on shopify already:

Monetization: You could take a percentage of revenue for every sale through the group buy system.

Steps to Launch: Ideally you would already have a shopify store to build, launch and test this on. By building it for yourself you would be "eating your own dog food" during the process and you would have a detailed case study once you're ready to bring on additional customers. I would start with an existing referral/affiliate program and adjust the marketing copy to add scarcity and manually credit their account. You could stipulate they need at least 3 referrals before they receive a discount and they have 12 hours to complete it.