I'm trying to find out whether or not it's possible to have autodj run only when the live source isn't running. I found this article: https://secure.centova.com/pages/faqs/display/how_does_the_automatic_live_71

But it's from 2009 so I'm not sure if things have changed.  So here's what I'm wondering:

1. Is this ability, as described in the article, still only available on icecast or can this be done on shoutcast now?
2. On either icecast or shoutcast, can I do this with aac+? (Meaning, since my live stream is aac+, the autodj that kicks in when I'm not live would be aac+ as well?)

This still works as described in the article, and no this won't work with Shoutcast. Also you can't use AAC+ with centova v2, though this may  be suported on v3 when released.

Yes AAC+ does work with the older Centova Cast, using sc_trans you can choose the encoder type in config > auto dj tab
 

Is there an ETA for 3.0??