The other major system affected by this would be Windows 2000, for which we already decided to not support it anymore.
Is there any 2000-specific code (as opposed to XP-compatible)?
Yes: a number of APIs didn't exist in W2k, so we currently use LoadLibrary/GetProcAddress to call them. These can be replaced with regular calls. _WINNT (or whatever the macro is called) then needs to be bumped accordingly.