Actually, after watching a few videos, it seems like it may be an autohandicap of sorts...It's obviously Sakurai's little way of saying "Don't dash dance! You're ruining MY GAME!"
It's not an advantage, it's a new approach to the "cheap" argument that I never thought we'd see. The producer getting directly involved
Just like declining damage and knockback is aimed at laser spammers and sword tippers.
I watched some Marth vs. Wolf vid on youtube, and the marth was ahead the whole match, and he was the ONLY one who tripped.
http://www.youtube.com/watch?v=JPO02OOtMFA
The tripping starts at 2:45 ish, after his 2nd kill to the wolf's first.
He trips 4 more time, twice in the three minute range, one late in the match.
My best guess is that it's an autohandicap.