We were always going to get a romance injected into the story, probably to tick the initial casting call (not just the Reddit guy's hearsay) included "Itaril" - an Elf of Mirkwood who was in love with an Elf lord (apparently of Rivendell from the male role description!) This was when GdT was still at the helm.
http://www.movies.spoilertv.com/...it-casting-call.html I think I'm right in saying that Tauriel only emerged after PJ took over. PB has admitted that they always wanted to expand on the Gimli-Galadriel relationship so that was the basis for the Tauriel/Kili storyline. We also know that Aiden Turner initially auditioned as an Elf so I guess he was always slated for the romantic "lead."
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