This might sound a little farfetched, but I think that every single npc character that's been available since New Leaf, including Gracie, Pelly, Phyllis, Pete, Digby, Kapp'n's family, etc. will be returning through the HHP dlc. At first I thought it might have been a stretch, but when I went back and rewatched the HHP portion of the direct, it hit me: there were no caveats. She straight up says to use figures and cards, and didn't list any exceptions. Additionally, as the narrator is talking, nowhere on the screen does it list or describe any limitations to the amiibo feature, meaning that as long as they have an AC card, they'll be included. With the exception of Wisp and Harvey(who are now in series 5) every single npc character that appeared in New Leaf had an amiibo card in 1-4, even Porter...
We may not see them doing much, especially in the base game(tbh, I think the only role they'll play is being able to come to the cafe if you scan their card), but it looks like every single card and figure, as long as its in the AC amiibo series, will be compatible with HHP.