Update 2: The Nexus 4 8GB model appears to be back in stock once again on the US Play Store, with a shipping estimate of 2-3 weeks.
Update: Apparently, some people are still seeing the 8GB version as still shipping in 2-3 weeks. However, if you actually attempt to place an order, you'll get the "An error occurred while processing your purchase. Please try again later" message. So, it's probably out of stock everywhere in the US, the change may just not have propagated across the internet quite yet.