Yeahhh.... We'll see if he wants to use Ridley's clone. Or Meta Ridley. It comes down to whether or not Sakurai finds it acceptable to tone down Ridley a dozen notches in order to turn him into a fair, playable character rather than a boss which would require almost no toning down.
Well, see, that's where we run into a problem. As a developer, yes, it's easy to just make Ridley a boss (see Subspace Emissary). As a businessman, however, you WANT the game to sell, especially the Wii U version. The Wii U version of Smash 4 is a risky investment because this is a game that Nintendo wants to move consoles. It doesn't have the benefit of being a novelty like the 3DS version.
How do you move your software AND your hardware? Listen to the fans.
We're already scraping the bottom of the barrel for playable characters, and that was after Brawl started doing it, so much so that Sakurai's already gone back on something he said back in Brawl's development days (see Villager). So now we're looking at this potentially occurring twice. Being the eccentric game developer that Sakurai is served him well the first three games. Now we're talking about a game that the fate of a whole console is partially hanging onto. Now is kind of a bad time for Sakurai to be putting in Wii Fit Trainers, Villagers and Chorus Men, but now's a REALLY good time for Ridleys, King K. Rools, Palutenas and Chroms. Y'know, characters people were actually asking for. Little Mac and Greninja were good first steps, but it's looking bleak so far.
That's how you sell a crossover fighter that's essentially a love letter to fans. Cater to the fans. Never minding that should be your goal from the get go, but there's only so many silly off-the-wall character concepts and clones/semi-clones you can put into your series before you have to step back and ask yourself why Melee and Brawl had hilariously disappointing rosters.
tl;dr: If you want to sell your crossover game, it's time to listen to the fans finally.
