It looks like Sledgehammer Games is starting to make Headquarters a social experience again. HQ was a solo experience for a while now as SHG worked to resolve server related issues.
PS4 players in North America, alongside players internationally, are reporting that the HQ is populated once again. SHG has stated that you may see players online while they continue to test out the experience.
Many players are now reporting that they are able to see 48 players in HQ and get back in other activities including 1v1 and more.
We will update this post with more info.