Back order is one thing, that would be a step up from the current situation, but they've had several models the have not been available for back order for weeks at a time... You can claim the blue was limited edition, but there's no excuse for not being able to place a backorder for any XL nor the 128GB 5" black model.
Basically you can order the small silver one, maybe black/32, and you're still looking at several weeks of lead time unless you go 32GB. To their credit they seem to be beating their ETAs by almost half the stated time, the ETAs are usually 3-4 weeks or 4-5 and many many orders seem to go out within 2-3 weeks.
That just shows their system is poorly managed and they don't quite have the logistics down, under promising and over delivering on ship dates is no consolation to the people that can't even order to begin with.
I'm slightly baffled (and annoyed) by the situation, particularly because the launch was clearly timed to take advantage of the holiday season and yet here we are unable to order about half the models and with Xmas rapidly approaching. Maybe demand has been stronger than they expected, especially in light of so many people looking for Note 7 replacements. Whatever the case, people are going to start looking at the 3-5 week shipping estimates in the Google Store and potentially decide to not even buy those models that are available because of the risk they won't arrive before Xmas. It's a bit of an epic marketing fail on Google's part IMO. In February or July, not such a problem. In November, a big problem.