From this interview:
In over a year since the premiere of Kingdom Come: Deliverance, Warhorse's developers have triumphed: they have overcome adversity, achieved commercial success, found themselves a publisher, which allows them to look into the future with optimism.
"What about modding support? How will it work?
Mod support is the last thing we are doing right now, the last thing we want to release for Kingdom Come Deliverance. Right now, we are working on modding tools so that people can do their own stuff – Steam Workshop is already working, but only with the tools you can write your own quest, for example. We are thinking of a way out to cleverly release that. Unfortunately, consoles are out because they're not supporting this – it's not because we don't want to, but because Microsoft and Sony haven’t agreed on anything yet, so I can tell you: PC – yes, and we’ll see about the rest, I’m not sure.
Ok, so if it’s the last think you’re releasing for Kingdom Come: Deliverance, I can probably scratch the Horse armor and battle royale DLC questions…
Well actually, if the modding tool is as cool as we hope it would be, then please do these kind of things, we are more than happy to support this."
Once of the subjects of our gamescom interview with Tobias Stolz-Zwilling of Warhorse Studios was the availability of modding for Kingdom Come. The developers are working on a set of tools that should give more power to modders, including the ability to create quests.