PDNguide (link is NSFW) spoke to Ned Bunnell (President of Pentax USA) during Photokina regarding the Pentax 645D release in the US :
"We're going to start to bring the 645D into the States in late November or early December but that's based on availability. We're still fighting fairly significant back orders in Japan."
The Pentax 645D will be shown at the PDN PhotoPlus Expo in New York in October. The US price will be $9999.99 for body only.