Github's core offering is a hosted git solution. I'm not sure how a crowd funding add on fits into that core offering.

Like another user already said, more money doesn't necessarily mean a boost in development speed/quality. I think there is something in "Kickstarter for developers" (there are bounty based sites that work like this), but I don't believe it really fits with the product/value prop.

I still think Github's biggest potential for revenue is from the enterprise-sized to medium-sized development shops, by way of creating software collaboration tools. Git can be hosted anywhere, but there are reasons why developers like Github beyond it being a repository.