http://bugs.winehq.org/show_bug.cgi?id=34593
--- Comment #4 from Anastasius Focht focht@gmx.net 2013-09-25 16:36:51 CDT --- Hello Austin,
--- quote --- I'm sorry, you're saying it would break things for 64-bit WINEPREFIXs? Or for 32-bit WINEPREFIXs? --- quote ---
Maybe the wording was a bit off - it might not really break prefixes but it makes things inconsistent from userspace perspective. Technically they have various differences in number of shipped userland components and feature sets (Wine doesn't make this distinction). Installers would really need to go through additional measures, e.g. looking at OSVERSIONINFOEX ProductType to disambiguate between 64-bit XP and Windows 2003 Server (WinVer and build numbers are the same) ... not sure if every app installer does this.
There were already attempts to get this in:
http://www.winehq.org/pipermail/wine-devel/2011-April/089681.html ("ntdll: Add support for Windows XP 64-bit")
Regards