The problem of open source is attribution, more specifically attribution back to individual contributors and the significance of contributions, and it is especially hard if you want to do attribution based on revenue performance if the licensee is small and do not have an audit department. A large proprietary software licensee can work with a licensor to track revenue performance because the licensee already have the right infrastructure to do so. So here is a startup idea:

An external auditing company with APIs to streamline the process of rev share and attribution back to the open source community and contributors, so that open source projects will make revenue and have the resource to reinvest and improve the projects.