In regards to the question about a BluRay addon, while it was hinted early on Microsoft might do it (I believe Microsoft said this when they had the HDDVD add on for sale), the answer now is looking to be no. Here is reasons why it likely won't happen, or shouldn't happen:
1. The number one home console, Wii, doesn't even play movies in North America (and likely Europe). I believe the Japanese Wii does play DVDs. So, what movies a system plays isn't as big of a deal for its sales.
2. The HDDVD add-on didn't sell well at all.
3. The cost for a BluRay add-on would likely be similar to the HDDVD add-on, that being around $200. It will be close to the price range for a dedicated BluRay player.
4. The BluRay disks won't be used for games at all, so not help there.
5. Microsoft is backing streaming and downloads now, as seen with Netflix.
6. BluRay read speed is too slow now to be effective for gaming. It can in some contexts, but apparently publishers are doing tricks with the PS3 version of multiported titles to get them to load up comparible to the 360. They also rely on installs of games for this to.
I am sure people can and have named other reasons. But as of now, it doesn't seem likely.
Now, is BluRay possible for the next generation on Microsoft (and Nintendo?). Well, possibly, if BluRay is the best storage medium for games you buy off the shelf. The drives are cheaper and have sufficient storage. Next generation will need at least BluRay storage, because 1080P will likely be the target resolution games will be designed to. As of now, high def market penetration is not there yet to fully support this.







