Yup these printers were hard to come by. But didn't help that people bought 3-4 and were selling BNIB on Craigslist.
Back to Instant Ink, yeah officially the OfficeJet Pro isn't eligible for the free 15 page plan. No option to choose it in self serve portal. But yes, if you call in, support can override this. I'm half done the colour cartridges in 4 months of use of Instant Ink cartridges.