"Dead horse, I will continue to beat you."
Even Microsoft recommends installing the 32-bit version of Office on 64-bit machines, because of plugin support. Windows x64 only is still 5-10 years away. Just my $0.02.
That is STILL rewarding developers for dragging their feet. How long has x64 been selling in greater numbers than x32? In the case of Windows, going back to Vista - in the case of Office, since Office 2010 - in that case, basically from the start, as 2010 was the first x64 version of Office. I don't reward foot-dragging by browser developers (and there is no longer a reason to, as the biggest culprit in terms of browser plug-ins - Adobe - DOES have an x64 Flash Player - for Waterfox), so why should we keep on rewarding foot-dragging by any other developers? Unless developers have incentive to move, they won't - and we ALL know it.
Threshold should include a warning for developers - WoW64 is going away with the next version; they have dragged their feet long enough.