The Boss says that the next kernel release will be 4.0, after a developers' survey that asked if they were ready to start a new numbering series. The next kernel would have been 3.20 if the devs hadn't voted for 4.0.
He says the new number series doesn't mean that much, except that "I can do releases without having to take off my socks again." If you remember, going from 2.x to 3.x was for much the same reason, as I reported here: https://www.aoaforums.com/forum/linux/49804-linus-cant-count-40-dubs-kernel.html
Interestingly enough, the 'strongest argument' for the new scheme seems to be that people have "a wish to see 4.1.15 - because "that was the version of Linux skynet used for the T-800 terminator." [The version of the android played by Arnold Schwartzenegger.]