With the surprises seen on the MS side of things at E3 thus far this year, I wouldn't put a BD drive in the "fairytale" pile quite yet (though I'm not saying they're currently planning it). At this present moment in time, I'm a big fan of what Blu-ray is capable of. I'm willing to bet that many of the problems we had with DVD technology will not be present in early Blu-ray activity, as Blu-ray was more thoroughly developed and planned. As we've seen with the 2 profile updates, Blu-ray has proved to be updatable without loosing playback due to early hardware adoption (while newer profile features won't play on older profiles, the actual movie itself will play, regardless).
I believe in 2015 we're predicted to have our content toting "4320p" tags, which means HD movies will potentially grow 8 times (or more) in size (not to mention bandwidth). It's possible that Blu-ray will no longer be a viable format at this point (possibly fluorescent discs, or protein-covered holographic discs,), though I don't know enough information to really qualify that. In the meantime, however, we've got 1080p, and BD more than does the job. I expect that if 2160p content surfaces in the coming years, Blu-ray should still be adequate.
Let's also not forget how much more the 360 offers over the original Xbox. While I'm sure the 360 will still receive support even in 2015, I'm also sure that Microsoft will have a new console available before then. They will most surely incorporate Blu-ray in that. As of today, they seem focused on digital downloads (most of which expire), but that certainly isn't stopping millions of people from purchasing higher-quality films on Blu-ray, and I'm sure they are aware there's at minimum a reasonable demand for Blu-ray among Xbox 360 owners. Perhaps when MS can effectively build a BD drive that they could sell for ~ $100, they will...perhaps...