Regarding the Minecraft content, couldn't it have simply been a red herring so that the validity isn't too obvious? I vaguely recall something like that from Pokemon SM where there was a leak that had everything right except for 2-3 Alolan forms (I remember Doduo and Growlithe being mentioned).
On the other hand, Smash 4 had a BitTrip Runner trophy and MS and Nintendo seem to be on pretty good terms with each other with all the current cross plattform gaming going on between them, most recent being Fortnite, but also, well... Minecraft and I think Rocket League? Especially when compared to Sony who seems to be against it and just does its own thing, so seeing something from Microsoft wouldn't be that huge of a scretch and Minecraft is pretty big. Although personally, if there's MC representation, I'd like it to be something from the Rare days, like Conker, Banjo & Kazooie or Joanna Dark.
At the end of the day, Sakurai is a madman and pretty unpredictable. He said Villager isn't a fighter in Brawl and yet he was the first to be confirmed for Smash 4. Ridley had been called too big by him for years and now he's in as well.
Moving on from the Minecraft talk, I indeed do not really understand why Sakurai is reluctant to include obscure Japan only characters as he said with Takamaru. Smash has the ability to make obscure characters much more well known. Look at Fire Emblem, Marth (and Roy) was originally intended to be exclusive to the Japanese version of Melee, yet was kept because the testers liked him so much. Look where Fire Emblem is now, being one of Nintendo's bigger franchises, just having had a game announced this E3 even. The same could happen to a lot of characters, like, for example, Takamaru, Lip and Sukapon. Maybe even giving them enough attention for a sequel or reboot. I'd go so far and say it even helped Ness and Earthbound, despite not being Japan exclusive. The franchise was still very niche back during the N64 days, having sold poorly in the US and not at all here in EU. In fact, I first got to learn about Earthbound due to Smash Bros. And now? Earthbound is a classic, even being released on the VC (which is a far cry from the Masterpiece in Brawl which was removed in international releases). Even the very first MOTHER for NES was released internationally as Earthbound Beginnings on the VC and I think it was the most downloaded title for a while.
In short, the marketing power that Smash has tremendous and can help old and neglected franchises a lot. I just wish that ability would be used more. Although I'm just glad to finally see Sukapon, Nintendo's first fighter, get some recognition. Even if I wanted her to be playable, I'm still glad to see the robot as an Assist Trophy and not completely forgotten.