I have had a oneplus one for 2 years, running cyanogen on it, and have gone through all the OTA updates to the latest 6.x based OS with no hiccups. My only complaint about cyanogenmod is their recent push to integrate microsoft onedrive services and other microsoft "cloud" stuff, which you can just ignore...
After that I never bothered with the OnePlus 2, the lack of NFC support probably had more with me not buying it than the OS support but that also played into my decision.