I wouldn't say it would be unreasonable to expect it to be at Smash Con,/ which really isn't a true major as it again a convention (and will run literally anything that's not Project M), it's just a lot of people end up attending Smash Con./
And as a T.O., at multi-game events that aren't literally only smash tournaments like EVO, it only makes sense to run the two smash games with the highest playerbase as now, Smash Ultimate and SSBM. As a T.O., it's also easier to run only these two smash games for logistical and monetary reasons.
And Brawl only had 3 majors last year, GoML, Smash Con, and Return To Subspace, 1 being a dedicated Brawl Major, and the other two literally ran every official smash game. Expect the same treatment for Smash 4, which ended on a rather poor note similar to brawl, and was replaced by a much more fun and balanced game respectively.
And 64 is like Melee or even Project M, as it's playerbase is extremely grassroots, so they found ways to host nationals throughout the games 20 year span, and spawn a very dedicated fanbase who travel to these events for a 20 year old game with little to no actual payout for years. Not saying it's not impossible for smash 4 to pull off something similar, but odds are very much against it. Smash Ultimate is not only very similar to the point one could say really it's just a Smash 4.5, most people think the games more balanced and fun. Smash 4 is also tied to the Wii U.