We have new word: http://www.technobuffalo.com/2016/03/25/oneplus-3-benchmark-and-specs-show-beefy-powerhouse/
This is looking promising. Snapdragon 820, 4GB RAM, 32GB storage, FHD display, sounds a bit like the OP2 to me. Announcement 7 April, that's interesting. This means it could hit before the HTC 10.
Things that we can hope for: AMOLED, Metal or glass build, Expandable storage, big battery, $350 or under. I don't give one about FHD, but it's interesting that they're sticking with it. Definitely won't make it underspecced or outdated, contrary to people's claims.
Overall this is shaping up to be a great release for OnePlus.
EDIT: Just saw an article confirming that it won't be announced on the 7 April event.
Staying at a 1080 display should reap performance and battery benefits. Also the costs as well. Impressive looking device to say the least at the pricepoint.