I think if there is ever an Oceania-themed expansion, the Inca would receive the new regional Drua ship, but they should receive something else too: an extra scenario tacked on to the end of the Pachacuti campaign.
Now, this has never been done before, and that one scenario may require a new narrator if the old VA can’t be rehired, but I think the scenario would add variety, and its focus would be on Topa Inca Yupanqui’s voyage to the Pacific. As Pachacuti’s son, there is that thematic relevance, and it would be nice to finish off the campaign in climactic fashion by taking the action outside Peru and fighting someone who isn’t the Inca.
Granted, the scenario should ONLY be added in the event of an Oceania expansion (since no existing civs can adequately represent the region), but that’s one more reason why it’s a good idea. In terms of gameplay, perhaps the endgame can be to collect a certain amount of gold, like in the scenarios of Tamerlane and Babur. That reflects how the expedition returned with a large number of gold, as well as many captives.
During my initial Standard difficulty playthroughs of all the campaigns, Pachacuti was the one I did last, which turned out to be smart, because it lacked sauce and was in general boring. The campaign as a whole will not be interesting until more South American civs are added, but an extra scenario focused on another region would help it stand out a bit more, as otherwise, it’s literally just Inca mirror matches.
As for the people who already have the achievement for beating the campaign, we can leave them alone. Only people beating the campaign for the first time would have to play the new scenario.