Previously the OnePlus community started the IDEAS Beta Run Recap campaign to allow OnePlus phone users to make suggestions, which included the Always on Display feature.
An update post for the OnePlus phone recently said that the suggestion to add the Always On Display feature has been adopted.
The post said, "Always on Display - development to be finished around June, CBT/OBT coming in Aug/Sep [subject to changes, there are various factors working]."
In addition to this, suggestions such as "add fingerprint lock for hidden images in the gallery," "add sound alerts when the phone is fully charged," and "add more features to Zen Mode" have been officially adopted and are expected to meet with OnePlus phone users soon.