But then how would you support choices or conditions for example?

Maybe something like this for choices?

    fruits = MultiChoiceInput
        # What are your favourite fruits?
        - [ ] Apples
        - [ ] Oranges
        - [ ] Bananas

Personally I'd prefer good old MDX though:

    <MultiChoiceInput
        name="fruits"
        hideIf={name.value !== "FruitLover"}
        options={["Apples", "Oranges", "Bananas]}
    />

Well, you can define the syntax however you like in a new DSL, right?

I like the syntax notpushkin proposed and would extend it a bit like this:

    fruits* = MultiChoiceInput
        # Pick two out of three fruits
        Fruits are healthy, so let's pick two fruits
        you will eat every morning for the coming week
        - [ ] Apple
        - [ ] Orange
        - [ ] Banana

All such text markup DSLs were invented at least once on usenet.