Unfortunately, I agree that Aurore and Mireille are probably one-time major characters that only had "Stormy Weather" as their time to shine, and the rest of their appearances from here on out will be background roles. Outside of minor speaking moments from them, like in "Dark Cupid" and "Pixelator", I can't imagine we'll get more moments further developing these two separately or together.
However, as far as headcanons can go, I'd like to hope they became friends, if they weren't already friends before "Stormy Weather". If they have been friends for the entire series, it would add an interesting personal layer to the KIDZ+ competition, Aurore upset that her friend beat her.
One way we could potentially see more of them would be if the classes are changed up for the second season—in Origins, Marinette established that the classes aren't set, so Marinette and some of her friends could end up in the same class as Aurore and Mireille, thereby allowing those two some more opportunities for development. (I'd actually be surprised if something like this didn't happen, because changing up the classes would allow them to introduce new recurring characters who could be akumatized.)