I was wondering about the union between Arwen and Aragorn. The point of that marriage may well be what Tolkien said in the appendix: "the two lines of the Half-Elven finally joined together."(that's not a direct quote, just an idea, I am too lazy to check right now.)
maybe Tolkien just don't want to deal with the Half-Elven anymore...he had to give them excuses for every choice they make...