Sephiroth’s splash image should have been “Sephiroth Gives You This Pear”. Honestly, I’m disappointed.

I’m going to presume the Geno Mii costume disqualifies the character as one of the last three DLC fighters.

I think that's a safe assumption. I think Mii costumes are Sakurai's way of implementing characters who didn't make the cut.

There's no Waluigi costume so there's still hope!

When the announcer stated "everyone is here" I genuinely though it was a reference to the Waluigi memes where he's left in the mud while that is being chanted.

I mean, there could be.  But I think Waluigi has been left out of the pool since he was confirmed as an assist trophy.  But it would make for the "ultimate" troll to have Waluigi as the final DLC character.  The trailer alone would be crazy.

The big news for me is we got more then 2 songs this time, and some are new remixes as well. 

Of course the Geno news is certainly a big one as well but not too surprising.  When Sakurai said Nintendo gave him the choices for DLC, that kind of hurt his chances.  The last 3 are probably going to be from famous third party characters, or from more recent Nintendo titles.  Poor Geno certainly had a lot of support online, but I imagine Nintendo wants characters that the general public has either heard about or someone who might introduce them to a current Nintendo franchise like ARMS which they're still selling at full price.