I'll let you into a little secret here, if you promise not to tell anyone else........................................ :-D
All the current screenshots would have come off of an Amiga with either a Voodoo or a BVision derivative. How do I know this? Well OS4 was not running on the AmigaOne at the time of the screenshots being published, so only the current RTG solutions would be available.
To be quite honest, I'd not worry about this at all. The initial release of OS4 will be for 'Classic' machines with PPC accelerators. Since owners of these machines will, invariably, have GFX cards, these will be supported first. As and when OS4 for the AmigaOne is finished, new GFX drivers (inc Radeon support :-D ) will become available. Even then, the new 3D GFX system (NOVA) doesn't look as though it will be ready for the initial OS4.0 build (probably OS4.1?), so initial advantages over the current cards will not seem that great.
-john