The absence of a Snapdragon 836 this year could be pushing OnePlus to gloss over its mid-generation OnePlus 5 refresh and instead pour more resources into its next major release for early 2018.
https://www.notebookcheck.net/OnePlus-could-skip-the-OnePlus-5T-in-favor-of-a-full-fledged-OnePlus-6.256142.0.html