Status update after today:
As of right now, local developer builds, the main waterfall, tryserver, blink waterfall, perf, and FYI waterfalls have all been converted to x64. A few more bot configurations need to be switched tomorrow, but the switch appears to be sticking.
There was a little bit of turbulence, so thanks to ncbray@, pdr@, phajdan.jr@, petewil@ and others for helping get through it. Things are looking greener now, but though.
I'll signal again when the transition is complete.