Well, it really depends on how much Microsoft thinks their XBox 360 gamers are using their console to watch Blu-ray movies.
What's the motivation for Microsoft to have an in-built Blu-ray player for their XBox 360 anyway? Even though HD-DVD was dropped, that doesn't mean HD-DVD games are going to die. Unless, the cost of producing games in HD-DVD is going up, or the cost benefit of having games in Blu-ray disc are better, there's really no reason why XBox games can't still be stored in HD-DVD.