Well whatever ends up happening im sure it wont be a blu-ray/hd-dvd combo drive as that will only increase the price of the console and next gen is gonna be about the price to performance/innovation. The cheaper the better. As i have said earlier Watching Hi-def movies is nice but not an essential feature so i doubt microsoft will support it.
And for all the people that are thinking bout them having a higher end/premium model with Blu-ray support think again because that would allow developers to use blu-ray as a medium for creating games and the lower model wouldnt support it.
If microsoft decides to go Blu-ray (which is highly unlikely imo) they will go all into it and throw in movie playback and games on Blu-ray. They will not use 2 disk formats.
Long Live SHIO!