I'm not actually sure what Layton would do...
He fences sure...
But what else could he do?
Considering the way Sakurai designed the likes of Megaman and Villager etc in this game. I'd expect Sakurai to represent Layton by what the series is about as a whole: The puzzles themselves. (For example, a sliding tyle puzzle animation for his throws or the magnifying glass for his grabs etc)
Seeing Layton fence around in a couple of cutscenes during the games is neat and all. But it doesn't really capture the full picture in terms of what the series is more or less all about and I would think Sakurai would understand that considering his track record with some of the newcomers we've received this time around.
If Layton where to use a few fencing moves. I'd expect him to have it sparingly and even then I'd think a lead pipe rather than an actual fencing sword would suit him better.
(At least a lead pipe is not a sword....)
And then of course there are the various contraption's he's made such as the town catapult, home glider and slot machine gun.
I can see Sakurai coming up with some very interesting ideas for Layton. After all, we've never had a puzzle solvng character in Smash before.
(Besides Dr. Mario but y'know.....)