I think calling them NPCs isn’t quite right. It suggests that they are characters of their own when I think we should be aiming for something a bit more static and machine like.
Taming creatures would be great, especially if they get round to adding some of the new races we’ve seen in concept sketches! It could be a problem for characters that aren’t hunters though. If you stay on low level planets then you’d basically be limited to an army of baby wildstock… (cute but probably pretty useless)
They could implement a system where one player can tame creatures and sell them to other players?
I think some kind of craftable robot/golem would make it more accessible. If you give them a variety of simple functions but limit it so you can only choose one or two at a time, and make them less effective than actual players, it should keep the whole teamwork/multiplayer vibe going 
Make them difficult to craft so a golem is a big investment for a player.
If you look at the concept art for the protectors race then that’s basically what I was imagining. You could either tame those, or drop parts when they are defeated and use to craft your own little robot. It says protectors spawn in temples and titans so still pretty high tier?
Just having them roaming around your settlement would add a new feel of life, even if they don’t do much 