The Humankind Devs stated in a live streaming interview that the Game was designed from the beginning to be modding friendly and they put extra effort for that. The Things that will be moddable, are (most of this won't be available at launch (although maybe yes, due to the delayed realease that might give enough Time to the devs to make these happen)):
- In terms of Values/Parameters and reusing stuff from the game (including Art Assets), like how we can change the Current Civ VI Database I suppose,
- Easy Moddable for any type of Modder (if you want to change some art/textures then you don't need to learn coding) with Tools from Unity,
- The AI will be completely Moddable,
- There will also be a Worlbuilder to make Maps. They put a lot of emphasize on Scenario moddability with the Worldbuilder (Players will have enough Possibilities to make any Scenario Possible),
- Making and adding New Assets to the game (like new Units/Infrastructures...etc),
- Changing the Map Terrains/Features/Biome and adding new ones with complete new Assets... etc
The Devs claimed that apart from the Avatars and UI (and scripting - but kept the option open (undecided), so maybe sometime in the Future, though), the Game will be pretty much completely moddable, eventhough the Tools won't be all available at launch. They also made a while ago a Vote of 3 Mod Themes to choose from (Fantasy, Sci-Fi, Alternate History) so they can make a Big Mod for one Theme so that Modders will have an Idea of what can be achieved with the Modding Tools.
Also, The Game is made with Unity, so the DLL files might be somehow moddable with some Unity DLL Modding Tools.
So if things go as announced/expected, then the Game will be much more moddable than Civ VI. But this latter has good Modding aspects, like UI, Selection Rules of some Art Assets, Scripting... to Name a few. Yet, it remains to be seen how Humankind is really going to be moddable

. That all sounds great to me, especially as a Modder, but I'm keeping my hopes low, till I have the Game and it's Modding Tools in front of my Nose.