Report transformations (or whatever we call it in the future) will be for reports only. But I think during data-entry, there needs to be similar concept developed where it would be possible to hook up Liquid markup which could modify form data based on input while doing data-entry.
You are thinking about this feature the right way (even if we don’t know what it should be called), it’s just premature when report transformations themselves are not complete yet (therefore not as useful as I want them to be).