> have they stated specifically what RadeonHD cards would be supported out of the gate?

Not that I'm aware of. There were statements about R700 (HD4xxx) support, but no confirmation as of late. Regarding pre-HD cards, see:

https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=11130&forum=3&start=18

...and pamper's posting just before mine :-)