But why?
Wing is the most similar position between league and union and he played union growing up so one would assume he has a bit of knowledge re: positioning and the breakdown.
If Cheika sees him outperform other Wallaby wing options at training why shouldn't he give him a run?
Koroibete's form in the NRL this year was miles better than Speights form in any Rugby he played this year (7s or 15s). It might simply be that hes the better option. It certainly looks like he has some class about him.
Maybe similar, but still many nuances about the differences, especially in defense. Look at Izzy when he came into rugby. Also started on the wing for the Wallabies after I think a full season of Super Rugby, and still had issues with positioning himself and with the intricacies of the sideline. As for his previous experience in rugby, that would just about be as relevant to playing in the Wallabies' structures in a test match as would be the experience of a colt just out of school and playing his first year with a back-of-Burke club.
He may in time turn out to be our best winger ever, though I very much doubt that, but he is an absolute novice atm at this level.
Barring injuries, one wing in the EOYT tests will be occupied by either DHP or Izzy and the other will be between Naivalu, Speight and Hodge (if Foley again slots into 12). How should we feel if someone like Naivalu, who has put in a couple of seasons at Super Rugby level while becoming eligible, misses out to Koroibete based on training sessions?