I wouldn't even give $400 for it, let alone $600. They need to learn that webOS is basically a completely unknown platform to the mainstream consumer. That's the reason why even the very known Android tablets have zero chance at outpacing the iPad 2, mainly because they are priced about the same. Just look at the Xoom. And what about those accessories? $50 bucks for a case? Seriously?
Asus saw this (as any smart company should), and priced their Transformer at a much much lower price. And guess what, they now have to increase production, because it has sold out.
The people that see this "webOS 3.0 tablet" --besides fanboys and enthusiasts-- will be uninterested at paying the same premium as the iPad 2, for a much lesser known device, whether it performs better or not (even though I know it does).