While the Starmobiles are nominally considered a form* of Revavroom, it’s probably worth noting that in the story, they’re actually a complex
hybrid of Revavroom, two Varoom, and Armarouge / Ceruledge. They’re not just a Revavroom with a big, gaudy, swappable exterior on them — which disinclines me to think that Game Freak would re-add them as more conventional forms.
* Though even in this regard, they’re different from usual. The Starmobile “forms” aren’t grouped with all the other alternate forms in the data, they don’t have names or even so much as empty spaces reserved for them in the common text files, which is something that even Koraidon and Miraidon’s various non-battle forms have, for some reason. Instead, the game basically just
modifies the data of whichever Pokémon was sent out before the Starmobile.