I think the best short term chance for 64 bit postgresql on windows is the upcoming SUA, aka Interix with the beefed up posix kernel personality that is coming out with the new server. The old interix had a full gnu toolset capable of compiling postgres. The neatest part was that they made it easy to swap out intel, ms, and gcc compilers.
That being said, from what I’m hearing it may be moot because it’s probably best to run postgres as 32 bit on a 64 bit operating system performance wise.
Merlin
It's very unlikely (in the near future that is). The current toolset we use is still well and truly 32 bit on Windows, and even once we've worked around that (by perhaps moving to the Microsoft Compiler), we'd still need to port at least libpq from PostgreSQL, as well as find 64 bit versions of the SSL and GNU Gettext libraries - neither of which I've ever seen.