Today's update brings about the idea of
Assist Trophies, which apparently serve the purpose of satiating people who wanted to see their favorite characters (who weren't quite brawler material) in the game, like
Samurai Goro, for instance.
I'd also like to note that since items are able to be turned off, and assist trophies and Smash Balls are items, basically everything new in the trailer is able to be turned off for tournament play. An amusing, but not very important, read nonetheless.