Make it open source and syndicate it. The goal is to get people to contribute both resources and code. Think about the Shopify as the model. Where many people contribute to create a huge shopping place. People care about their shop only but ultimately they create a useful shopping area.

Also setup a foundation to guide its development and be able to hire a management team.

The real challenge is not the code development but setting up an organization that will outlast all the challenges that will appear. Wikipedia is the model to follow.