One of the problems with consulting is that it's really hard for most people, while employed, to line up enough work that they can become consultants in the first place. Most people will never get the chance, even if they have the talent, because they can't front the initial financial cost. This keeps a lot of people out of self-employment who would otherwise be a better fit for it.
The Kickstarter-esque idea seems strong, but the biggest problem with this idea is that people who have serious ($150+ per hour) work to offer generally don't solicit on the Internet if they can help it. They prefer to source through word-of-mouth, which is pre-technological and broken and leads to that imbecilic situation where you have to be in to get in... but I don't make the rules.
That's why I haven't pursued it. It's one of those startups that requires fixing people, and any startup that goes long on human nature is facing extremely bad odds.
That said, someone who wants to make this transition needs to save enough for perhaps 3-4 months of not having a salary. If they can't pull that together, there might be deeper reasons behind them sticking to a salaried position. It's not likely the availability of work, because right now there are so many more opportunities than there are capable applicants in tech, you'd have to be trying hard to not find opportunities.
Factually, the problem with the idea you present (Kickstarter-esque capacity scheduling) is that every freelancer is different, there is no apples to apples comparison possible. Likewise, are you going to take every customer that is willing to pay you? I sure hope not.
I recommend that you block off some time and read The Win Without Pitching Manifesto. It is free online and seriously worth your time if you plan to work as a freelancer.
If I pledged to a kickstarter project to buy yet another iphone case and the project failed to launch, I'll just have to make do without yet another iphone case. No big deal.
If I need to hire a consultant to build an e-commerce website or to set up a payroll system, I need that to happen no matter what. I can't wait 21 days only to find out the consultant never gets enough pledges to "launch." Then what? Pledge to another consultant, wait another 21 days and rinse and repeat?