It's 1:20 AM and after about 5 hours of pushing and tugging I managed to finally get Unity Hybrid ECS working. Every guide on the internet is filled with outdated crap, and one of the last results (which is not mentioned in the official docs) is Unity's in-house samples, which are up-to-date. And it's actually really fucking simple.

I'm experiencing an emotion that's right somewhere in the middle of euphoria and bloodrage. But at least I can now make steps towards integrating ECS into my game.

edit: On a related note; is there still a difference between hybrid and pure ECS? The only way I can see people actually doing this is by converting their GameObjects to entities with a script in the Entities package, and then squishing pure IComponentData's in ComponentSystems.