Why not? If anything it's just as likely as Mario to receive a 5th rep, i don't see why you would think that.
Link - Main character
Zelda - Damsel in distress/Main female character
Sheik - Dunno why, but she's in. It's cool so whatever
Ganondorf - Main antagonist
Toon/Young Link - Basically different incarnations of the Main character.
Vaati - A bad guy twice. . . on two Loz titles not many people have played/less played than TP/OoT/MM ect.
Tingle - Only viable choice IMO, but definitely not "needed". Has a major role in his own games, not the LoZ universe
Zant - Ganondorf Puppet
Midna with or without wolf Link - A one timer who's probably not going to show up as a main character ever again
Majora/Skull kid - Shows up as skull kid often, but never as major as a role as Majora had. Now, if MM3DS comes out, his chances may go up. But still, not a main character.
Ghirahim - As far as I can see (Which isn't too far mind you) he's going to be a Midna, Zant, Majora. Nothing special
Toon Zelda/Tetra - Meh, less important than Toon Link, more important than Tingle, but the lamest character ever.
Just like Toad, and Jr. none of these characters are needed. While they are cool, we have a few smaller franchises that should take priority IMO.
I may even enjoy playing as him or her,
IF it happens, it will be a her. I'm betting on that. Not adding Pal/Med before Magnus would be like adding Bowser Jr. Before Bowser.