Skyrim will get mod support when Skyrim Special Edition launches on the 28th October 2016. It will also come with native 4K support for PlayStation 4 Pro.
Mods created using the Creation Kit will be able to be used on PlayStation 4 as long as they use assets that come with the game. Custom asset uploads are not supported.
Once the work with Skyrim is complete, Bethesda will work on bringing mods and 4K support to Fallout 4.