Fair's fair. Frankly I'm not ruling out Nintendo revealing the game play themselves. I just feel the information rollout might not follow the same pattern we're used to.
Food for thought while we're on the topic of Directs, depending on when the next one is held, it does raise the question of whether a March Direct is even a guarantee. If you look at past Direct schedules, barring Nintendo's E3 Directs, we only get two "general" Directs per year nowadays. Last year we only had a March and September Direct, though January did have a "Mini" Direct. In 2017 there was also only two general Directs (plus the Switch live presentation and E3). There's still a bunch of game specific Directs obviously, but I reckon Smash will get itself an E3 mini Direct the same way it got back in 2015.
I wouldn't be shocked if 2019 similarly also only has two general Directs throughout the year, plus E3, so unless we get another Direct Mini this month, I'm expecting March to not have a General Switch Direct - but I would assume it's going to have to be a big Direct soon because their 2019 schedule so far looks really empty and only Yoshi has a date. Based on what people have been saying, they have a big year ahead, so there's most likely going to be a Direct soon.