Doesn't really concern me since I don't plan on purchasing/using Amiibo, but I suppose if people don't want to spend the extra money (which I'm sure most probably won't), then they should just stick with the Link Amiibo they already have, assuming of course that it'll be compatible with non-Smash Bros. games.
It might be cool if they make limited edition Amiibos or something that have a cool Zelda-like design on them (perhaps a Triforce, as you said) that they could package in box sets to be released with the game, that might be neat.
As for including characters that don't currently exist in the Amiibo lineup, I'm not sure why they would. I suppose it depends on how Amiibos are used though. I would assume that only a Link one would work, since he's the playable character, but perhaps players can use Amiibo to make NPCs more powerful? It could work I suppose, but my main concern is about using an external item to power up a character you can't even play as.
Of course, there's also the possibility of making a multiplayer feature that utilizes different character Amiibos in a neat way. That might be cool, though I don't really forsee it happening.
