With all due respect, the idea that open source projects are always the result of free, volunteer work is a bit of a sheltered and idealistic view.
Open source projects with the most tractions are either sponsored, or someone is writing open source code as part of a job they're paid for. (a few examples: Rails, node.js, Linux, Vagrant ....)
For projects where that's not an option, crowdfunding is a good alternative.
Most "involved" in open source are consumers. Crowdfunding allows for involvement and support at a different level, and is totally consistent with the open source ethos. Open source is about freedom, not money.
