RIALTO or some other bridge works with AMD's new mainstream and entry level DirectX 10 cards. We confirmed this from various sources and there is still a big upgrade market targeting these cards.
Radeon X2600 series based on the RV630 will come in AGP flavour and of course even the entry level sub $100 Radeon X2300 series based on the RV610 works with a bridge chip.
AMD has the design kits for a while and this is a fighting chance for the APG market to go for DirectX 10. The cards are expected in May / June time, and they will be bit more expensive then the PCIe brothers.