Source is pretty much any of their video updates. Try some of their early one if you want to be specific.
But the writing and the quests we see in 0.4?
Well yes, it’s exactly that. Demonstration, they try to make the quest, or specific type of quest and see how people will react on them, their writing, their structure, , etc… If people love them, they might appear in the main game. They might purposefully create the quest, so they discover which types are popular, or what writing works, what doesn’t, etc…
Seems to me it’s a lot of writing and quest designing to be thrown away afterwards.
THey won’t throw away the resources they put into it. But those specific quests might not appear in the main game, in this form.