I love the idea, but I'm a bit worried that it's just webkit. Aren't all the other browsers important too? This is why I feel that Selenium still has a place, even though I agree that Casper is easier to use. Perhaps browserling is an appropriate answer?
I don't mean to disrespect CasperJS or PhantomJS, they're certainly wonderful tools, and any final automated functional test like this is infinitely better than none, but it's bad enough that people are developing for Webkit, do we really have to make it explicit by only testing on Webkit? ;)