You are right and it would have to be more than a business model. This would have to be more like a marketplace like Salesforce w/o the limitations Saleforce puts on developers. The marketplace would offer enterprise clients brand recognition and invoicing on their terms. This would make it easier for enterprise clients to buy the software.

I would have to be able to offer developers something as well. Why would a developer pay me x% of sales just to handle invoicing with the client? If I could offer the developer access to client org charts for example, then the developer has something to build software around that would be difficult to obtain otherwise.