They are a common tool to amp up the story. He already had one in Maeglin, or
what would be Maeglin. I guess changing him to be a love intrest instead of a
brother made for a better story. Though why Tolkien then made him less
important I don't know.
I would have loved for Thingol to had a son. I imagine his death would have had
to occur during the Ruin of Doriath so Dior would have claim to be king. And as
for Turin, his story might have been somewhat similar to Tuor. Turgon had an
heir of sorts in Maeglin but he slowly favored Tuor. I would think Dairon and
Turin would have butted
heads.
There, peeping among the cloud-wrack above a dark tor high up in the mountains, Sam saw a white star twinkle for a while. The beauty of it smote his heart, as he looked up out of the forsaken land, and hope returned to him. For like a shaft, clear and cold, the thought pierced him that in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.
The Lord of the Rings: The Return of the King
Book Six - Chapter Two
"The Land of Shadow"
