You know, as neat as the Mii costume is, I'm actually getting more worried about Isaac's DLC chances the more GS stuff is shown in base: what do they save for DLC? I hope my theory still holds true, but it's a little unnerving, to me, at least.
At least before, instead of being "suspiciously absent", Isaac was "suspiciously present", as it was just his Assist, and a couple spirits. However, now we can see six different spirits, an Assist, a Mii costume, and two songs: the Brawl remix, and probably Weyard again from Dark Dawn. (I was going through the music file name list and saw ont_overwold which I assumed to be Oogon No Taiyou Overworld, which is probably Weyard)