Okay, so my epiphany... Every pass has had only two returning Mii costumes from Smash 4 at most, right? Let's dissect this:
Joker- Knuckles and Tails
Hero- None
Banjo- Protoman and Zero
Terry- Akira and Jacky
???- ??? and ???
Going back to the Power of Six Theory, there's decent evidence that every Pack was originally going to have 6 Mii costumes.
Based on how Joker came out supposedly before Season 2 was green lit during the summer, makes sense that he's a perfect 6. Hero only has 4 with coincidentally the only possible returning and logical Mii costumes in the pack being Geno and the Chocobo hat. Banjo's a little tricky. He has five but also two returning Mii costumes, Zero and Proto Man. This stands to reason that there was originally 6 and, based on the numbers, was probably also another Capcom given it has four left at this point. This then fits in line with Terry, two returning Mii costumes Akira and Jacky with strong conjecture that Heihachi would have been a third based on the theme. Now, let's check our notes on what's left...
Three Capcom and Two Namco. Insert this into a hypothetical #5, this leaves only 1 empty spot for a full costume pass, probably one for the Namco series. Under this train of thought, it would be 3 Namco and 3 Capcom. Perfectly balanced and all Smash 4 costumes have returned.
Now, what does this mean? If Heihachi was "subtracted" from Terry, could it stand to reason that he would be added to 5, especially if the original plan seems to heavily imply that Gil and Lloyd were originally going to be Mii costumes for #5? In this new scenario, Heihachi and Gil are the most likely "+2" for returning Mii costumes because, all in all, Lloyd had the biggest chance of being promoted by a long shot, making his absence similar to Geno. Another thing to note, Gil and Lloyd are sword fighters, along with two of the remaining Capcom Mii costumes, both Monster Hunter ones. Seems to be a theme... Curious...