Microsoft won't do that for some time, if ever. So far, they don't need it to sell the XBox as a gaming console, and they aren't about to cut and bail after investing so much in HD-DVD. While HD-DVD may go away, it doesn't mean that they will get a Blu-Ray drive for the XBox 360 anytime soon, if ever.
On an interesting, factual note (since the XBox statement is still speculative), you can preorder a Blu-Ray internal drive for your PC for less than $200. Not too shabby. Hopefully this will drive the prices down again...