This is stuff people have waited impatiently for going on six months or more, and it's starting to come together. I'm continuing to work using Prototype/Scriptaculous and put together a simple Autocompleter mixin. I've been working on a more general Ajax operations, wherein a link on the page will trigger a component event and the return value there (usually a Block) will be used to update a portion of the page (demarked by a Zone component).
I'm also simplifying a bunch of APIs that got twisted up for PageTester (Kent Tong's unit testing layer for T5). ActionResponseGenerator is going away which makes a lot of code and testing easier and simpler.
Right now the only thing slowing me down is some soreness in my left hand.