Honestly, it sounds too safe to be true. People'll start believing it for a bit if Dedede gets revealed and that's probably all the guy wants. Once people start believing him, he'll release some "new information" that's more controversial and which'll get people talking. They seem like they're just wanting to start something, honestly.
From what I gather, it looks fake, although the person did their research, unlike most rumors on the rumor thread.
I do agree with you; it's too vague, and it only really has that one kicker (the Dr. Mario part).
That kicker isn't even a definitive kicker.
When the Brawl rumor came through, we got the Pokémon news first.
It had few pieces of bullcrap news:
-Pichu is gone. Most everyone in the know figured as much.
-Jigglypuff was returning. Almost everyone figured as much.
Then we got an interesting but predictable tidbit:
-Lucario is going to be playable
Then we got a juicy detail that really people couldn't get over:
-Mewtwo wasn't playable.
That was really how you do a reveal. That was mind blowing back then. I still can't believe we learned that like 3 or 4 months before the release of the game (in Japan).