The reason why I believe the jet black is popular is because throughout the leaks, most of it was for the matte black (aka space black). I believe the manufacturing for the jet black came late into the stages. That's my theory why it has become so scarce and Apple probably didn't expect it to become so popular. Jet black was probably a late edition and unexpected success.
If you don't plan being an iPhone 7+ scalper, I really don't see anything bad at waiting for it even if it takes a month or so. Give it some time to iron out all the bugs. Look at Note7 owners. It took only two weeks until Samsung did the recall. Who knows what early issues and -gate problems comes out of the 7? Your delivery might be delayed, but you still have time to cancel your order and change your mind if you don't like what you see.
Patience is a virtue. This is basically what early adopters are for these launch days...
Yup, guinea pigs to do some beta testing for you. They pay all that money to be the first owning it and then the first to experience problems. That's like signing up to be in the front line during a war. Chillax. Wait for all the reviews and early issues to be sorted out. I bet some people who had their Note7 exploded on them wished they waited.