You have a good idea here but it might be ahead of its time.

How are you enforcing the contract? How is the bitcoin held once received in order to enforce the contract?

It's a great deal for the payer because they have only potential upside and they are paying anyways so they just use fiat buy bitcoin and wait to see if they get any money back. The receiver on the other hand doesn't get the bitcoin until the end of the contract term. Maybe they don't care because they are hodling anyways but if they need liquidity for any reason they can't sell or use the bitcoin as collateral.

My suggestion is to try to get others to pay you this way to further prove the concept so you can see what kind of roadblocks and issues you might run into. You can still work on building out your app. You are just the beta tester.