Ya well opinions can let us say dang near anything, lol!
But yeah, sursly!
PEOPLE OF UUURRRHHHH!!!
In terms of relevance to a franchise and popularity, the only character on that list that comes anywhere near to competing with Ridley is Dixie Kong. Even though she is great, and important to the DKC franchise, she hasn't been as popular as Ridley has been in about a decade, when Donkey Kong fell off the face off the Earth thanks to the breakup and sale of Rare to Microsoft, and a small studio called "Retro Studios" rebuilding Metroid for a new era in Metroid Prime (and Samus' chase to find Ridley and that epic Ridley boss fight being a part of it).
I honestly have troubles seeing any 1st or 2nd party character being more worthy than Ridley (a 5th Generation and/or possibly once they are created, a 6th Generation Pokémon aside) to appear in the next smash bros. games. He is Metroid's Bowser/King Dedede/Ganondorf.
Heck, Ridley has appeared in every Metroid game but Metroid II (short and had severe limits), Metroid Prime Hunters (takes place in another universe), and Metroid Prime 2 (which there is data of him in). That's 3 out of 11 games he doesn't appear in.
Ganon (called "Gannon" in the original Legend of Zelda) or Ganondorf didn't appeared in Zelda II (aside from the death screen), Link's Awakening (aside from Nightmare's form of him), Majora's Mask, The Four Swords, the Minish Cap, Phantom Hourglass, Spirit Tracks, and now probably Skyward Sword. That means Ganondorf only appears in 1/2 of the Legend of Zelda titles.
Granted, the Legend of Zelda is like a 3 or 4 times bigger franchise than the Metroid franchise. However, Metroid is too big to have representatives that aren't Samus to be ignored... unless we get like Zero Zero Suit Samus, or some other random power suit of Samus (which totally won't be a new character; maybe an alternate outfit).
Ridley has supplied me with 9 years and just shy of 11 months of "Why isn't he in the game?" sadness. I am still mad that my friend told me Ridley was in Melee. Worst. Fake Rumor. I have been told... EVER!!!!!!!!