OK, we've decided to release the first beta of AIM 6 (AKA "Triton") to the public!
Note that this is a very early beta, of a product that is a complete rewrite... it's not very polished in a lot of places. The standard disclaimers about beta software definitely apply here.
That said, you can see it's going to be a really good product. A whole new UI engine, called "Boxely", IE as the IM renderer, a new IM library called AIMcc with plugin support - we've got a solid foundation to develop on.
For those interested in the plugin API - take a look at the type library in acccore.dll. Plugins aren't exposed in this beta, and the API isn't final, but you can get an idea of what is going to be supported by this API.