Except Ridley didn't even have massive wings in his more well known appearance (Super Metroid), as well as Metroid Zero Mission. The large wing thing is a Metroid Prime thing.
I can't see Ridley being that hard to make playable if Sakurai: 1. Wanted to make him playable, in the first place. 2. Realizes the freaking huge wing spam thing isn't a defining characteristic of the character and 3. Realizes his size isn't a defining characteristic either.
The major problem here is Sakurai actually wanting to further represent Metroid, imo. It doesn't seem like he is very fond of it (and Donkey Kong). I mean, I am not saying Ridley would be the easiest character to make, but in a game that have or had characters like Pikmin & Olimar, Ice Climbers, Rosalina & Luma, Pokémon Trainer and hell, even Mr. Game & Watch, I doubt Ridley would figure among the hardest characters to make playable... if only Sakurai wanted to make him playable.