Import Taxonomy data on new field instance

I'm finally able to get back to using this module (thank you, #319724: only unset taxonomy form elements that would conflict with content_taxonomy fields!). Because I haven't been using this module, I have a lot of data in term_node that I would like to port into the fields I create with this module. Single-term fields aren't a problem with some simple SQL. However, multi-term fields take a little more processing, and it would be nice if there was an automated way to populate the CCK fields.

The thought is (and excuse the idea if it's already come up) to allow the user to import data from the selected vocabulary when a field is instanced (not just created, since it can be shared among multiple content types, each possibly needing to be imported). This could potentially improve adoption of this module, since there wouldn't need to be any kind of extra data-fiddling when someone switches to it.

This could be done with an extra checkbox when the field is being created, with a label like "Import data from the selected taxonomy?" Then, using the "multiple items" setting and the selected vocabulary (and possibly the hierarchical settings), on field save migrate that data across. The actual interface could be done however (button instead of a checkbox), my only additional request would be that any processing uses the Batch API (I'd be willing to help with this) -- I have so much data that it would certainly timeout if left to just a regular form submit.