If Apple feels that the current iPad Pros can make it for longer than one whole year (which is very possible considering how long the first-gen 12.9" one lasted), then it's possible the next generation ones be released after the 2018 iPhones, so they might go from the A10X to an A12X. I mean, the A10X is already kind of an A11X in a way, since it's a 10nm chip, unlike the A10.