So just to recap on what we know so far -
Roger over at Roger's Base, a person who is seemingly known to have sources within NoA, tweeted about learning some really exciting Nintendo news that he's not allowed to come out with. However, within some closer circle of his it seems like the news spread a little bit, and at least
Stealth (another person who has had industry sources in the past) and
Zef (a Smash scener) have seemingly found out about the news from him. It should be noted that those two are the only ones who explicitly mentioned it to be Smash news and that Roger hasn't mentioned anything about it being Smash (also pointing out that he doesn't know anything of the Smash Ballot's outcome). That said, a tweet aimed at Shofu did hint at another "Japan Time" going down. Zef also made the point that this information ain't likely to leak unless the source comes clear with it, as there was nothing recovered from the last patch to suggest that the character is hidden away like Roy/Ryu. Warchamp7 (SmashBoards admin) also seems to think Zef as a trustworthy source since he acknowledged the mills they were spinning. Either way, all signs point to this being some kind of Smash news and that it has to do with a Nintendo newcomer who is likely to cause a lot of buzz despite not necessarily being the most voted for.
"So why do we assume it's Splatoon?"
The game is evidently poised for another major update soon as the person who has been datamining the game for a while is expecting a major update to hit in mid-October, and that might have to do with Octolings being playable in the game. That said, with the Smash rumors now circulating, they seem to be convinced that this is going to result in a major Splatoon Direct that details the news and reveals them as a playable character for Smash. Again, this is speculation, but what it boils down to is basically a truckload of "where there's smoke, there's fire". With the Inklings meeting all the checkboxes that the tweets mention it seems like something bigger might be in store. GameXplain also raised the point that Nintendo don't really have much of a holiday schedule at all so it'd make a lot of sense to leverage their existing products (Smash, Splatoon) with a lot of DLC going into the holidays.
I don't know where that leaves the Shovel Knight rumor personally. I could make the assumption that if he is in he'll be slated as one of the "ballot newcomers" maybe later next year. It seems somewhat reasonable that he might still exist in some form (especially considering how passive Yacht have been in regards to talking about the ballot compared to WayForward who wouldn't shut the fuck up about it and begged people even in Kickstarter e-mails to vote for Shantae) but that if that would ever be true, it would still be ways off. I'm personally indifferent about the veracity of that rumor though.
Incidentally as I'm writing this,
Smash is scheduled for another online maintenance tomorrow. Presumably something to do with that 1.1.2. Diddy patch.