When do you think we will get the starters final forms as their sub type.
Ghost decideueye dark inceneroar and fairy primarina.
Ghost decideueye dark inceneroar and fairy primarina.
Eh, Vileplume we kinda did. We got a couple of Psychic-weak Vileplume prior to Diamond & Pearl, where Poison was still part of Grass. (The Delta Species one was also, ironically, Psychic-Type and weak to Psychic.)
Keep in mind some Pokemon represent one of their types a lot more than the other, though. I wouldn't expect something like a Colorless Mantine or a Fighting Carracosta to be terribly likely, for example. We've gotten a surprisingly large amount of the potential "alternates" at least once, though. It's mostly only Pokemon that gain types via evolution we lack at this point. (That said, the Gen 7 starters are in that category too.)
I wouldn't normally consider weakness as a determining factor, either. But it's the only way certain Pokemon (such as Grass/Poisons prior to Diamond & Pearl or, say, Gengar now) could have their alternative typings, so I do consider it valid for those cases.
I disagree with Skarmory and, especially, Skymin. I'd say Skarmory's Flying attributes aren't much less prominent than its Steel ones. (Incidentally, I wouldn't consider most colorless Flying-types surprising in general, as most are birds, which makes their Flying types pretty prominent. There's only a few bird Pokemon, like Zapdos, that I'd consider to represent their main type more.) Skymin in particular kinda needs to be Colorless to stand out from Landmin. (I'm actually surprised we've gotten as many Grass ones as we have.)
Carracosta I view similarly to Omastar. We might get a Fighting one eventually, but it would be a weird, once-off. Same goes for Bastiodon and Cradily.