As of this weekend, you can now apparently book Hawaiian and British Airways flights using your aa miles on aa.com.
The web interface has also changed:
Until this weekend, the circled text below said "AA and Alaska Airlines". This change will make booking partners using aa miles much easier. It would be great if they add all partners soon, as the new text suggests, if one reads it optimistically.
If you click on "List of Participating Award Carriers" you get this:
I couldn't find any announcement of this on the AA web site, so I have no idea if other partners will follow.