It would be possible for MS to allow Bluray to be used for games (although I don't think they would - it'd be an admission that not putting a highdef drive in the 360 was a mistake) provided there was an external Bluray drive accessory. That would be no different to some games (e.g Football Manager or Worldwide Soccer Manager as it's known in the US) being unplayable without owning the optional hard drive accessory.
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