Think about the following example:

shirtsize:
    default: m
    label: What Size Shirt Do You Wear?
    type: select
    values:
      s: Small
      m: Medium
      l: Large
      xl: Extra-Large
      other: other

Wouldn't it be cool to have a text box appear next to a select box when someone chooses "other" (the way the next level of a pagepath appears after you populate the previous level)? There are loads and loads and loads of uses for data forms where a select box seems more appropriate than a wide-open text or wiki box, because there are a few options that collectively encompass the vast majority of people's answers, but not necessarily all of them. This could be implemented in any of the following ways:

    label: What Size Shirt Do You Wear?
    other: true
    type: select

which would just automatically add an other option to the list of options

    label: What Size Shirt Do You Wear?
    otheroption: 8
    type: select

which would recognize that a selection of 8 was effectively choosing "other"

etc., etc.

This would add a lot of power to an already powerful data forms toolbox.