To be honest, I think it's still possible for Ridley to have multiple roles, i.e. playable and a stage hazard. It would kinda be like Toon Link with that 3DS exclusive stage Spirit Tracks: when someone plays as Toon Link, he isn't part of the stage, when no-one is playing as Toon Link, he is part of the stage. Or better yet, Bowser was a boss in Super Smash Bros. Melee for Adventure mode. When you fought him, he was bigger and a more regular canon size, but when he was playable, he was his scaled down self. Oh, but "Ridley can't be both" say the detractors, "he's the exception". I'm sorry, but who's making the game here? It's rather annoying that the Ridley situation is being dragged all this time. I can only think some reasons why (I'm probably repeating myself, which in this case, sorry):
~ Sakurai didn't want to show Ridley at E3 because it would've impacted hype.
What I mean here, is that whatever Ridley's role is in the game, the news would have possibly taken the spotlight away from the newcomers shown at the event (Palutena, Mii Fighters, Pac-Man). If Ridley was shown as playable, people wouldn't care so much for those other characters, and the discussion would have gone to Ridley (though it should). The same would happen if he was shown not playable, except being shown non-playable would have made some people lose interest in the game. Sakurai probably wanted to hype these characters, not have something overshadow them (I'm... so... sorry...). None of those 3 characters would've stood a chance.
~ Sakurai probably wanted to not show unplayable Ridley at E3 in respect for Ridley fans.
In the unfortunate event that Sakurai has chosen the lazy copy & paste route of Stage Hazard-ly (basically copying what a third party developer has already done), Sakurai probably didn't want to reveal Ridley at E3 in case it made people de-hype. De-confirming Ridley in a PotD pre-E3 is bad enough, but de-confirming him at a big event would've been twisting the knife. It would be much, much worse post-E3 now that we're edging towards the Japanese release date. He might not even talk about Ridley until after the 3DS version is released, so if there's no PotD or mention in the estimated August Nintendo Direct, then we won't know about Ridley's status until post release.
+ Sakurai possibly has something planned.
Which could be playable Ridley. Tricking people into thinking Ridley is some stage boss, when he could be playable instead. The ultimate troll. Or Ridley has multiple roles, both playable and as a WiiU exclusive stage hazard. It would be rather bad to hype up a character that would end up not playable. Apart from Yellow Devil (which let's be honest, no-one expecting it in the game, let alone playable), no popular character has been hyped up this much and then confirmed not playable. That just seems wrong, if you want to hype something as a boss, you show that boss, THEN you talk about what they do a while later (like with Yellow Devil). So wouldn't it make sense to hype up a character (months of teasing) that's both playable and a stage hazard? Perhaps Ridley's time to shine is in August.
+ Sakurai might want to keep Ridley's playable status hidden (until after release).
This can also link to the previous point. If Ridley is playable, Sakurai could have planned to be keep Ridley as a secret/hidden unlockable. R.O.B. was confirmed to be an enemy for the Sub Space Emissary, via the Dojo!!, but after people played the game (and after he posted the respective secret character page on the site), people discovered that R.O.B. was also a playable character, but a secret unlockable.
- Sakurai is a cruel, cruel man
He likes to keep people on their toes, and likes seeing people argue. He enjoys the Ridley debate so much, and he's waiting for a chance to twist the knife. Choosing to wait until the week before the 3DS version's Japanese release, he posts a PotD detailing a Stage Hazard-ly (even though he had the whole year to do so). He likes to watch fans of characters suffer.
Though I got the impression that he doesn't like letting fans down, and seems light-hearted. I think he must've regretted that PotD with Waluigi, though it might have been a combination of a translational error and the wrong interpretation from the fans. If he de-confirms Ridley in a harsh way, whilst giving other dis-confirmed characters a lighter, easier, and less painful dis-confirmations, then I don't think I'll know what to think of the man. Nor will I ever trust him ever again.
- Sakurai is just deluded and thinks that we're okay with a Stage Hazard-ly
Yeah... he might just think we'd be happy with whatever as long as Ridley's in the game. He is wrong. W-R-O-N-G.
If I can think of anything else, I'll post it later. Case in point, I hope Sakurai is hyping up a playable Ridley, or even a multiple role Ridley (Playable and WiiU exclusive stage hazard), otherwise I will not impressed by this amount of teasing for him to then reveal a non-playable boss hazard only Ridley =/