They do not look that badass on low, which is what a WC3 version would have to be due to the lack of features like only 1 texture map supported.
However the reason they can not be exported is not because it is impossible to do, it is just impossible due to legality reasons. Giving WC3 people free axcess to models that SC2 players had to pay to have axcess to is piracy, which is illegal.
Its just like why WC3 models can not be used in SC2.
Ofcourse if blizzard says we can do it, it is no longer illegal (some WoW icons in WC3) however I highly doubt they will do that for ported SC2 models to wc3, afterall they did not even do it for WoW models to WC3.