One thing about your final point: you should probably be asking yourself why you need a web application that doesn't act like most web applications. If you don'

One thing about your final point: you should probably be asking yourself why you need a web application that doesn't act like most web applications. If you don't have some really compelling story that you just can't (reasonably) tell in traditional HTML/JavaScript/AJAX applications, there's a fair chance you're just going to piss off a lot of your potential users, who expect a web site to act like a web site.