Hello.
For future challenge ;)
I wonder is it possible to add XML transformation by XSLT at end of advanced import process after MAPping Attributes and maybe configurable product generate to use MAP and configurable to predefine XSLT schema for easier editing. In this moment we would know which source attribute assign to known magento 2 attributes and after configurable product part we know how generate configurable product -maybe adding some pattern to configurable part ;)
In fact tht XML is advanced csv formt i think that would be good way to add conversion from CSV to XML and ability to use XSLT to CSV files and maybe other supported formats ;)
I don't saw anywhere which version of XSLT is supported 1.0 2.0 or 3.0?
For Export XSLT support would be also good advance ;)