You're right that most existing web application frameworks (targeted at lisp or otherwise), use some sort of server side state mechanism. But that is not to say, that a rapid prototyping framework couldn't be made, which used solely client side state.

Anyway, I am of course putting it a bit on the extreme end here, but in principle I stand by it. Continuations are but an elegant hack; I might prefer it over other similar hacks, but I'd rather not have to use it at all.