Ok guys, seriously, calm down. New person comes in asking about Ridley, you don't say it was a mistake to come to the Ridley thread. That's the point of the Ridley thread. This is where anyone can come to talk about Ridley, not where we punch people who have different opinions, or are new. This is sometimes a big problem 'round here. This guy is pretty obviously new to the boards and safe to assume not a troll.
Well he did mention bosses while showing his shadow and Boss Hazards seem to be the big new thing. He was secretive about Yellow Devil so he is probably being secretive here as well.
I'll give you a good answer here. Ridley wasn't actually shown as not playable. That's Sakurai's trick. He talks about Boss hazards, then shows a characters shadow. So the first logical assumption is, that character is probably a boss, right? And I agree, that would make perfect sense, if not for a single fact. Sakurai is a giant troll.
Did you notice the other troll things Sakurai did during the event? Saying Zero Suit Samus was cut? Showing the fake Palutena trophy, but making us think it was real, and then later showing Palutena as playable?
From this we know that Sakurai likes to troll about playable characters. Well, Ridley's history of trolling actually goes back way further than this direct, all the way back to when the Pyrosphere was first shown, over a year ago. On that picture of the day, Sakurai said
"An enemy from Samus' past may appear at any time"
hmm. So we know, on the Pyrosphere, Ridley is a boss character, and may appear at any time. Well, on the Super Mario Bros U stage, Bowser is technically a boss character (he is a character that is a boss), and is an enemy from Mario's past, and he can appear at any time (that people choose him). And also remember, Ridley also wasn't shown during a boss hazards segment. He was shown during a Stage segment.
So we never have Sakurai actually saying that Ridley is a boss (or even showing him at all, for that matter), and we have a history of Sakurai trolling. What does it mean?
We don't know. We can't know until either a boss/character reveal, or the game comes out. But we certainly don't know that he's deconfirmed.