Would label::... columns not work with these questions? It can sometimes be useful to given different human-readable labels to data columns which can be used for visualization / exporting into different languages. I believe this is possible for other hidden questions like calculations. Not a big issue though.
Partial audio recordings
This is not part of the spec yet obviously. As mentioned elsewhere, from a user perspective I would find it more intuitive to specify the start / end of a background recording by adding a start / end point to the form, rather than what you proposed in the Extensions section. This could work like groups, e.g.
type|name|
--|--|--
background-audio-start|recording1|
text|
...|
background-audio-end|