Another hour or so later, all four combinations (16 or 32 GB in black or white) were again available with a note that they would leave the warehouse by November 8. It's likely that these stock and shipping statuses will continue to bounce around for a while.
Within only minutes of the launch, shipping times began to slip to a week or more.
I've reached out to Google for clarification on Nexus 5 availability. It's happened with past Play Store launches that an "out of inventory" message appeared prematurely due to heavy inbound traffic, and it seems that's what's happened here as well. So keep checking back and refreshing that Play Store link as well as checking back here for updates. I'll update this post when I hear back from Google.
Updated at 1:25 p.m. to reflect that all Nexus 5 models were again in stock.