I've seen a lot of videos of that demo over the last day or two, and this is what I know.

-Jill from Drill Dozer and Little Mac from Punch Out! are assist trophies.
-Gardevoir is in a ball, and uses barriers to block projectiles.
-Meta Knight's voice is awesome.
-Ike is a powermonger.
-Peach's Final Smash involves dancing in the center, damaging everybody onscreen and putting them to sleep, while dropping peaches (surprise, surprise) to heal.
-Meta Knight's Final Smash requires a bit of accuracy to pull off, and he makes the screen blacken, and then slashes through it and damages anybody nearby.
-Ike's Final Smash involves electricity, but I've yet to see what it actually looks like.