This is my opinion about what Sega's announcement will be. Someone claiming to work for has already said Sega will team up withan unnamed console maker to co-develop a console. But what is that company? I believe that Sonic already gave the name of that company away. Sega will codevelop a console with Sony, and exclusively make games for it. The gpu would probably be PVR-based. And do you remember Sony very recently licensed PowerPC? The main cpu will probably be a PowerPC. But why would Sony want to team up with Sega? Don't they already have the Cell-based PS3? Well, I can think of two reasons:
1. The rumor that Microsoft and Nintendo will share a commpn next-generation platform is true, so Sony needs to respond to this threat.
2. Perhaps Cell is turning out not as powerful as expected as I have speculated previously. And perhaps now that Sony has an idea how powerful Microsoft Xbox2 is going to be, they need to develop a completely new console quickly.