Mega Bidoof
Smash Hero
I would love to agree with you, but unfortunately, the most likely Zelda newcomer is Tingle.Wrong thread.
New topic starter: Tetra is the most likely Zelda newcomer.
Tetra has great moveset potential, a unique playstyle, looks completely unique, and does will with the "4 pillars of success."
Appeal: The release of WWHD, even with less sales, has resparked interest. The prospect of playing as a pirate is very appealing. It's also a strong, less-girly female character, which some folks might feel is missing.
Style: Definitely would fit in smash, and the WW style is already immersed into Smash.
Unique: She's quite unique. There's some similarities with Sheik, but the radically different artstyle (and presumably, radically different physics [and radically different moveset potential due to lack of usable legs]) makes her quite different. Simultaneously, the pirate idea is pretty much a new one, and another female character is, of course, more unique than another male character.
Balance: It would help balance out the roster by making Toon Link less of an odd duckling, and allow for a "realistic vs toon" dichotomy to exist with characters that are technically "Zelda."
And to add with it, a Skyward Sword zelda artstyle is very unlikely. It would be very difficult for SS zelda to transition into Sheik, with Sheik given a "Shoo-in" pass, and it wouldn't be very unbalanced to see cartoony Zelda stand next to realistic Link.
As much as I hate Tingle, and live Tetra. Tingle is the likelier of the two.