[Angelic Cross]

Uh, it didn't confirm

Spoiler for masked character:

that it WAS Marth, just that said masked person is claiming to be Marth.

Plus the official site lists the masked character's VA as Yu Kobayashi. Now isn't that interesting?

Spoiler for Another theory:

After all, Marth's regular VA is Hikaru Midorikawa. Now, here's another theory. The masked character is Marth's FEMALE descendant who decided to use his name for her own goals.