I don’t see why it would be any more complicated than importing news stories from PostNuke or other similar data imports. Just need to read the data out of whatever docVar table structures there are and then store them into the TV structure. Something like the PostNuke Import Tool I started to author, and contributed here somewhere might be useful to get you jumpstarted, though you’d obviously need to understand both the source and target data structures well enough to modify the code for your purposes.
In fact, I’d like to tackle that as a proudly displayed utility or add-on for MODx; convert from Etomite DocVars! I hate for people to have to suffer like this when they really have little chance to know that MODx exists...or that DocVars was the original inspiration for what is now known as TemplateVars

If someone will add it to the task list in Flyspray as a feature request...