That seems like it'd work, but I'm not sure what is gained by replacing Kickstarter with a smart contract (as opposed to replacing Kickstarter with a centralized alternative)
The advantage would be avoiding the 5% Kickstarter fee + (according to Wikipedia) 3% to 9% payment processor fees. The computation fees charged by the blockchain are presumably well below that. [On the other hand, maybe they aren't. Calling this suicide function on the Parity multi-sig wallet apparently cost 27 cents. If the crowdfunding contract is more complex, and submitting a payment costs, say, a dollar, then the average contribution would have to be on the order of 10 dollars to break even vs. Kickstarter.]
You can save the cost of Kickstarter by removing the value Kick-start adds. You get a smart contract that can't be executed because no one decides if the project delivered properly. How is that an improvement?
> no one decides if the project delivered properly
Same as Kickstarter. They release the funds to the creator after a certain deadline, after which they do not get involved in deciding whether the project delivered. Which is what I wrote above.
EDIT: I should add that I do very much agree with the general point you're not making: Smart contracts are only smart inside the closed world of the computer system running them; they don't magically know things about the "real world", and they cannot affect the "real world". I agree that many smart contract aficionados act as if they didn't understand this basic point. That's why I deliberately chose the Kickstarter example, which is also a system that does not make guarantees about the real world once payments have been made.
What the smart contract can't do is ensure that the funded project actually delivers on its promises. But neither can Kickstarter...