I'm not going to get my hopes up too much, but I'd be very surprised if we didn't get at least one character revealed.
I would expect it to go something along the lines of.
1) Start with a character reveal, maybe clone, but overall a safe bet character (Isabelle/Pokemon). Nothing too mind-blowing, but to get everyone excited.
2) Thank the viewer, share their excitement/enjoyment/gratitude to be working on the project with so many talented people, etc.
3) Cover stuff we already know, mostly filler, maybe showcase stages we've seen in character videos/screenshots, cover items/ATs/Pokemon that the Treehouse covered, go over some tweaks to the cast
4) Showcase some new content, probably new Donk City stage, a couple new ATs, possibly some unrevealed new or returning stages, go over the character revealed at the beginning
5) Announce and cover couple modes, either brand new or returning
6) End with a big character reveal, something to get the fans talking, either a really popular pick, a really unexpected pick and/or a third party character. Also, this character would totally be unique and not a clone/echo.