AJAX is a pain in the ass because it essentially means you'll have to write two sets of similarish code: one for browsers with JavaScript enabled and those without.
Not only this, but you have to connect JavaScript events to hook into your models and display the results.
And if all that weren't bad enough, you need to send an address change with the request, otherwise the user won't be able to "click back" correctly (if confused look at what happens to the address bar when you click links in GMail).
We're searching for something that had the foresight and design goals with all these concerns in mind.
Performance and security are also obvious major concerns.
We love config-based systems as well, where you don't have to write a lot of code you just drop it into an easily read config format.
It's like asking for the holy grail right?