Thanks for your question.
Good news! Coincidentally the pulldata() function was just added to the new Enketo last weekend, funded by Ona. It requires the very latest Pyxform (XLSForm convertor), which is still undergoing testing before it is deployed to the various tools. Old forms will have to be re-converted/uploaded.
The other 2 external data functions that ODK Collect has, i.e. the search() appearance and the select_one_external will likely never be implemented in Enketo because of a
strong technical disagreement. It would weaken Enketo's engine considerably and eventually catch up with the project. Instead the new Enketo has a solid alternative for this (which
hasn't been added to pyxform yet, so can only be used in Aggregate for hand-tweaked XForms at the moment).
Cheers,
Martijn