I wonder how flexible they can be with the height of the Deluxe costumes... they are all clearly in the same height/body range (Geno would be the next logical fit for this)... I think at this point it's more fun to try to predict who the remaining Deluxe costumes will be. Isaac as a Sword... is he too tall? Shovel Knight as a Sword would be perfect. Ashley, Jeff, Knuckle Joe and Prince of Sablé could also fit and not look ridiculous regarding AT's.
There's no way Isaac would work as a deluxe mii costume. I would say any human character likely wouldn't work as a deluxe mii costume. (unless they're already a chibi style human and even then I'm not sure if it would look right because a deluxe costume is basically a helmet that gets put over the mii fighters head)
I think the human characters would be way more likely to fall into the uncanny valley if they tried to make deluxe mii costumes for them. So I think even Ashley, Jeff or Prince of Sable could be a bit awkward looking. (Knuckle Joe might be too short)
I'm not sure if Shovel Knight as a sword fighter would actually be perfect....so far the deluxe costumes have done a decent job of representing the characters. Sans and Cuphead as gunners....and Bomberman as a brawler, while not perfect...at least he doesn't have a weapon for no reason.
Shovel Knight on the other hand doesn't use his shovel like a sword at all. I think he'd end up being the least "immersive" of all the deluxe costumes.