No matter what game you play it will always be mods for it old or new, but it all depends on the people if they enjoy the games.
Complete isn't good. At all. In fact it's worse than we where dealing with now in ue3. I doubt anytime soon mods will come, more so since the files are different for ue4. No more UPK. Maybe if people play it for costumes, screenshot, fashionista like me then maybe you'll see mods, but even then we need to deal with anti cheat nonsense to which could be difficult.
The only thing people have done so far was open the .pak to see the games contents.