I'm a really big ZeLinker, but Skyward Sword is the only game I'll admit to the pairing having a good chance of actually happening. With the other games in the series, I just see Link and Zelda as cute together -- there's really no canonical evidence that's enough to support the pairing. The ZeLink in SS was pretty obvious, but as always, it's up to each person's interpretation of the story. I'd love to see Link and Zelda end up together canonically, but I know a lot of others wouldn't, so really I think it's a better idea to keep things the way they are when it comes to romance in the series.
I don't argue with canon couples, so Pipit and Karane are sorta just there for me.
I don't exactly support Fi x Ghirahim. Sure, they're both sword spirits, but does that necessarily mean that they should be together? That's like saying Groose and Peatrice should be together because they're both humans. (Nothing against the pairing; it's just that that reasoning seems a little... silly.)
Although, I agree. If Fi x Ghirahim happened for whatever reason, it would be the most hilarious thing. Imagine Fi giving Ghirahim a statistical reading for every single thing he does...