I really don't think we're getting anything. I'm convinced it's not happening.
However, I did speculate earlier today why that rumor might have been plausible. It's kind of clear that right now, for the time being, we're not going to get any general Directs. We've gotten two Mario Tennis trailers, Tri Force Heroes info has been dropping left and right and we've gotten a bunch of info on stuff like Yo-Kai Watch. The weird "thread" I found to be consistent in all of this is how this only started after the rumor originated, which was specified as a Splatoon Direct. Why would the rumor be so specific about it when it'd almost be even safer to assume a few weeks ago that any information we'd get around this time would be in a general-purpose Direct?
And the weird thing is, we did get an update for Splatoon - but it only contained trace data amounts of new content that was going to be added and a lot of it was structured as if most things had been ripped out of it. There's only two or three new pieces of actual gear, and usually when Splatoon gets gear updates it tends to be in a bigger bulk than that. Stage data is in there, including NPCs for them and some details about the gimmicks of them, yet there are no actual models. Only one new weapon is in there and that's actually an unspecified leftover from 2.0.0. On top of that the animation data for Female Inklings (a file which is shared with Octolings) was edited, which is the only animation data in the game that was altered.
So really... I could believe that Nintendo would be planning an information dump for Splatoon. A lot of what's there suggests that we should have gotten more information for that game, both through circumstantial occurrences and the actual data we received, since Nintendo knows that the dataminers tear through the game like hot knife through butter and might want a more controlled environment for details. For that game, I still believe we're going to get another update down the line so to some degree I'd still see the basis of the original supposition. It could very well be delivered in another Splatoon Direct too considering they could present that under the Squid Research guys or even through a Callie / Marie staged segment. It wouldn't have required figuring out how the stage presence was going to be and I think it's one of the only few "Directs" they'd feel comfortable with doing.
But again, at this point I really don't believe the rumor right now as it was presented and whenever we do get another update, I don't believe that Smash will have much to do with it. It'd be a really nice bonus, but at this point it's best to let go any expectations.