Camera quality is still being improved for the device and compatibility issues are being worked on. This update also fixes the WhatsApp crash issue for parallel apps, which will certainly be helpful for dual-SIM users running separate WhatsApp accounts.
As per OnePlus’s announcement post, the OnePlus 3/OnePlus 3T will receive 2 years of software updates and then another year of security updates. The devices have already received their last Open Beta update, and are scheduled to continue receiving regular updates until November 2018 and security updates every 2 months until November 2019.
This OTA is also being released as a staggered rollout, with a broader rollout in the coming days assuming there are no critical bugs. OnePlus notes that the VPN trick may not work to get this update quicker, but users can expect to see download links for sideloading the update in our forums soon enough. This OxygenOS 5.0.4 release also attempts to migrate users from the Open Beta branch to the Stable branch. If you are on an Open Beta release, do note that this update will require a clean install with a data wipe. Curiously, not all Open Beta features have been mentioned in this changelog, so it remains to be seen if those will be ported over to the Stable branch eventually.