Yup. In fact there is work underway
now on complete templating, database persistence and state
Here are some links relating to what ruoso said:
Ajax Massive Storage System
(supposedly simulate a database without RDBMS or web server).
The point is that "offline AJAX" is a buzzword to be looking out for. Another buzzword "serverless AJAX" might become popular. In fact, with JSON, you can have "offline AJAX without XML" (which is ironic, since XMLHTTP is what started this whole bandwagon in the first place).