A side note with Mii Costume theory, I did some digging to see which Mii Fighter costumes were already added to the game prior to DLC.
To my knowledge, the only ones added prior to DLC are all of the Nintendo owned ones. So that's the Takamaru, Isabelle, K.K. Slider, Link (now BOTW), Captain Falcon, K.Rool, Ashley, Chrom, Dunban, Toad, Smash Bros. T-Shirt, Viridi, Business suit, Samus, Black Knight, Bear, and Flying Man. Each of those was DLC for Smash Wii U/3DS, and is now included in the base game.
Literally all of the remaining 3rd party DLC Mii Fighter costumes, coming from Capcom and Namco Bandai, were not included in the base game or with 3.0 Update content.
This more or less furthers the idea, at least to me, that these updates are being advertised as packages. You get the update regardless, but with the update you get a ton of thematic content. We're missing content from Namco Bandai and Capcom.
if they aren't with the 4.0/Hero update, or the 5.0/Banjo-Kazooie update, it would make logical sense, at least to me, that these properties (Namco-Heihachi, Lloyd, Gil, probably others) and (Capcom- Mega Man X, Mega Man Battle Network, Proto Man, Monster Hunter outfits, Zero) would come as a part of their corresponding bundles.
But I'll leave it at that. It's not fact yet, but I think it's got a logical chance of occurring that way.