I think the era of platform games in general is over.
I wouldn't really say that, considering last year gave us DKCR, Kirby, Sonic Colours, all 2D platformers.
I'm guessing if they put 3D platformers on the 3DS, emphasis will be on depth. Pretty sure I read somewhere that they experimented with Yoshi's Island to test the idea out.
As for whether Zelda should go sidescrolling... Well I did rather enjoy the sections in Link's Awakening, and it'd be kind of cool to see that again, but a whole game? Probably not, but I wouldn't rule it out entirely.
Honestly I think Zelda should get some sort of spin off that strays a little from the norm. Practically every other game series has one (the Pokémon Ranger/Dungeon to the main games, the Kirby Power Paintbrush to the Dreamland, the Mario RPG/Sports Sim/racer to the typical platformer). The closest Zelda has is the Tingle's Rosy Rupeeland series, which, let's face it, struggles to appeal to the hardcore Zelda fans let alone newcomers.
So yeah, as a spin off, sure, but as a main game? Probably not.