This looks cool, but I can't see why contributors should assign you copyright so you can sell proprietary versions of VirtKick. Very few free software projects have copyright assignment requirements (GNU being a notable exception).
CLA's are both good and bad. The good thing is that the software project has more flexibility when it comes to licenses, but the bad is that they have more flexibility when it comes to licenses...
We don't intend to sell modified proprietary versions. In fact, we planned to re-release it under MIT. Just see on the bottom: "Get excited: (...), MIT..." http://goo.gl/w64Ic5 from https://www.indiegogo.com/projects/virtkick-take-cloud-back We'd just want to get funded, so we can work on it without worrying about other things.