Yes default values and pulldata() functions can be used on select one question types, or on following questions based on the answer of a select one.
I'm not sure I fully understand what you mean here "in my case, I need to collect new features, but I also have an incomplete dataset of existing features Id like to auto-populate known attributes for into my survey".
The only way we support incomplete choice lists (lookup lists) is using the 'or_other' option. We do not support building up choice lists on the fly (adding to them) as the survey is being completed and then having those new values added to choice list to be able to be selected in a following questions from same choice list. Is that what you meant?
Regards,
Phil.