I think your suggestions affirm my statement.
Many of the characters you mentioned are very weak. These isn't a strong Metroid character outside of Ridley (one reason why everyone rallies behind him). Kid Icarus has a lot of characters, but most of them are very young and not proven. Mother really lacks anyone memorable, and Wario is a joke in comparison (are we really gonna say Mona is a stronger character than Goroh?) When you stack them together, Black Shadow and Goroh are very strong.
The fact that you can only come up with weak choices makes me believe two F-Zero characters are very likely.
No offense, but that really sounds fanboyish towards F-Zero.
As yes, there are Metroid characters that are strong; Dark Samus is a major antagonist of an entire trilogy of games (she is the Metroid Prime, after all). Mother Brain is also a strong character who's only problem is how she would work, given that there's "brain in a jar", "brainasaurus rex", and "android with AI influence".
The issue for Kid Icarus doesn't call for "proven", as this is Sakurai we're talking about. He MADE the characters for Uprising, and thus, HE decides if they've "proven" their worth, not you or I. And also, there are two still that have more than just Uprising in their repitoire; Palutena and Medusa (Hades taking over villain role in Uprising aside).
Mother has plenty of memorable characters yet to be included. Most notably Porky, who
can work, if Super Smash Bros. Crusade shows (if that is too awkward, Earthbound Porky would seem more reasonable). Then there's Giygas, who can be incorporated in his Mother 1 form with his Mother 2 form being a Final Smash. Claus/Masked Man is also very notable with being a major character from Mother 3. And even if he looks just like Ness, there's also Ninten.
As for Wario, don't jump to "X from Series A is "stronger" than Y from Series B". No one's saying that. I'm not saying Mona is "stronger" than Goroh. I'm saying that within their series, they are equally as strong. Goroh is essentially the #2 in the F-Zero series with Falcon being #1, and Mona is essentially the #2 in the WarioWare series with Wario being #1 (with Jimmy T. being a very close #3). And then there's the fact that Ashley is the most popular WarioWare character in Japan and has made a bit of a name for herself during Brawl speculation...(So she's the "Black Shadow" of the Wario series, in this case)
But anyways, you kind of overstate how important the characters are.
Outside the anime and games that specifically involve the anime, B. Shadow is just another bad guy racer. There's nothing that puts him above Zoda in F-Zero X, and in F-Zero GX, right away, we see Black Shadow as a mook for the Big Bad of the game, Deathborn, who in turn is a product of the Bigger Bad, The Creators. So in the one game that had a story, he made himself more important than Zoda at least; but in the sense in how Bowser Jr. is to the Mario series. If we specifically go by the anime, then Nightmare is a "strong" character for the Kirby series, or within the series itself, it would make Jody Summer a "strong" character, as she is one of 3 main protagonists of the anime, the other two being Rick Wheeler and Captain Falcon.
Goroh's only importance is that he's been in the series since the beginning like Falcon. But then, that would make Pico and Dr. Stewart equally "strong" within the series. I guess what puts him above those two is that he has a direct rivalry with Falcon (even if it is one-sided). It also helps that he's in Melee's opening as well as having Assist Trophy status in Brawl.
And as others have stated, Sakurai doesn't seem like he's going to add that many characters this time around, at which point, having TWO F-Zero Newcomers causes a drop in favorability towards another series even getting one character, be it veteran or newcoming series.
So like I said, it's going to be one or the other if F-Zero does get a new character. Could be B. Shadow for his anime popularity, could be Goroh for what Sakurai has done with him thus far. My money's more on Goroh.
