Keep in mind that, until very recently, Master Chief was second only to Goku in terms of meme characters that are "never getting in." Outside of Smashboards, I think I've seen maybe two people total ask for him unironically. And even here, I think it's more that people expect him and are getting hype because of that and less that they actually want him. It's another case of the Erdrick effect.
Besides, if Sakurai really has access to the Xbox family of characters, I really doubt he'd go for Master Chief over the former A-list Nintendo mascot that people have been clamoring for since at least Melee's pre-release. He may not look at internet scuttlebutt, but he certainly looked at the fighter ballot and Banjo-Kazooie was one of the top picks there. Certainly bigger than Master Chief, who was basically a non-entity.
Even if Fatmanonice is blowing hot air, even if this brave new world of Backpack Redesign Speculation ("BRS" hereafter) is just a series of goofy coincidences, we still have IndieGamerChick, whom most of us agree is legit and doesn't seem like the kind of person who'd fabricate hype for the attention. The only thing she's said that maybe indicates that "coming home" thing (something that definitely couldn't refer to Master Chief, btw) was a bust is that we'd be hearing about it "any moment now" in March, but c'mon, it's not like two months and change is such a long time that she couldn't have been talking about E3.