As Gamespot notes, Layden said in 2014 (yes, 2014) that Sony had to take steps to prevent griefing. It didn't want trolls to cause havoc in one game, change their name and promptly ruin someone else's play session. There's also the matter of making sure that all your friends see the change. It's unclear whether or not Sony might ask you to pay to change your handle, as Microsoft does on Xbox Live (again to discourage griefing), but setting up those exchanges could involve some work as well.

There's no guarantee that Sony will have name changes in place. As you might have noticed, it's been talking about the idea for years. The narrow time frame suggests the feature is getting close, however, and it's easy to see this becoming a higher priority given that a PSN account is increasingly vital to making full use of your PS4.