I think ownership and time are the major impediments. As an investor in a company, you're going to invest more than the small amounts that change hands on kicks

I think ownership and time are the major impediments. As an investor in a company, you're going to invest more than the small amounts that change hands on kickstarter, which will probably mean you want some degree of assurance in return for your money. So there's the equity part, which could be tricky to try to automate. And time wise, the projects that come up on kickstarter seem to be much shorter term than a startup would usually be, which just underscores the need for equity as a more formal commitment. I'm sure there are ways around these issues, and I think it would be great if someone (you?) sat down and figured them out. But these are the reasons why it hasn't already been done, imho. If you can make it work, I'll definitely use it!