This update about Fallout 4 PS4 mod support was supposed to be launched in June, but there was a delayed, but there was an assurance that it has not been canceled.
There was a report that the Bethesda Softworks executive of marketing named Pete Hines explained that the said mod support is still ongoing, and so it is not canceled at all. Also, according to the Metro, Hines implied that one among the causes of this delay is due to Sony and the process of evaluation. Sony will want to make sure that mod support is free from any glitches and so will run smoothly on PS4, PS4 Pro, and the PS4 Slim. Along with that, Sony would want to make sure that accounts at PlayStation are indeed safe from those hackers knowing the fact that mods might lead to identifying theft and some other forms due to hacking.
There was also speculation from the fans that the mod support for the Fallout 4 is important for the Bethesda Softworks knowing, that the approaching re-master of the Elder Scrolls V: Skyrim has dubbed the Special Edition. And will bring mod support as well and so will not go by that smoothly up until the mod support for this Fallout 4 is not yet completed. Therefore, the speculation also led to the idea that this PS4 mod support would be launched before releasing the Special Edition of Elder Scrolls V: Skyrim which would happen in October.