> I think this iMac G5 support has been on the pictures teasers since ages or not?

Yes, it has. For more than 2 years actually:

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7638&start=46

Working links to the pictures:

http://tunkki.dk/~cyfm/iMacG5-1.jpg
http://tunkki.dk/~cyfm/iMacG5-2.jpg
http://tunkki.dk/~cyfm/iMacG5-3.jpg
http://tunkki.dk/~cyfm/iMacG5-4.jpg
http://tunkki.dk/~cyfm/iMacG5-5.jpg

> Anyway is their any SPECIFIC model that has been announced to be supported?

I'm not aware of any announcement regarding iMac G5 support. However, the teasing pictures above show this model:

http://www.everymac.com/systems/apple/imac/specs/imac_g5_2.1_20.html