As per my other post, don't hold your breath. I'd expect PS 6 to do the same in fact, along with lots of other new versions of things.
Setting an OS minimum that is < 10 years old is not unreasonable in modern IT environment. (In my oppinion)
What they do with PS CS6 doesn't bother me much as I won't bother to upgrade anyway.
The point regarding XP is that it still has a huge user base, despite it's age. It was still being supplied as the installed OS on many systems just two years ago.
In my custom profiling business I've dealt with more XP users in the last year than any other OS variant.
I'm puzzled what feature arrived with Vista that is so necessary to LR4 that they'll abandon such a large market segment.