I love rumors!!!..... don't you?... try this one.

[BottledSpringWater]

One point is really interesting.
IF they do release a Blu-ray add-on, it will void the argument that PS3 is the only console with Blu-ray. I mean, a big selling point for the PS3 is the Blu-ray. If it is provided to 360, then there's really no argument there :S
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Thanks!