OPPO has announced its two new devices, the R15 and R15 Dream Mirror, in China. If history's anything to go by, the upcoming OnePlus 6 will share a lot of similarities with these devices, including a notch and a 3.5mm jack.
https://www.notebookcheck.net/This-is-the-OPPO-R15-which-likely-also-doubles-up-as-the-OnePlus-6.289940.0.html