Hi R: Those are interesting points, but they seem to be in conflict with some others:
For instance, immediately after the vision of Elijah with Moses and Jesus on the mountain (Matt 17: 1-8) we read "10And the disciples asked him, “Then why do the scribes say that first Eli′jah must come?” 11 He replied, “Eli′jah does come, and he is to restore all things; 12 but I tell you that Eli′jah has already come, and they did not know him, but did to him whatever they pleased. So also the Son of man will suffer at their hands.” 13 Then the disciples understood that he was speaking to them of John the Baptist." (It should be noted that John had been killed by Herod shortly prior to this point.)
And earlier in Matthew 11, Jesus says:
13 For all the prophets and the law prophesied until John [the Baptist]; 14 and if you are willing to accept it, he is Eli′jah who is to come. 15 (A similar discussion is found in Mark 9:11-13).
I think the answer to this confusion is found in Luke 1, when the angel Gabriel is describing to John's father, prior to John's birth, some of the aspects of John's upcoming life:
16 And he will turn many of the sons of Israel to the Lord their God,
17 and he will go before him in the spirit and power of Eli′jah,
to turn the hearts of the fathers to the children,
and the disobedient to the wisdom of the just,
to make ready for the Lord a people prepared.
This quote seems to address your question about how Elijah could be "birthed again."
And John the Baptist was correct to answer to the priests and Levites (as you quoted above) that he was not Elijah physically (since the priests and Levites were more concerned with physical things). But, according to Gabriel and Jesus, John was indeed Elijah if you are looking at the spirit. And most of Jesus' teachings were about spiritual realities.
So, to return to my original question: Some Christian communities anticipate that at least the spirit of Elijah (or the spirit of John the Baptist) will return in some form prior to the return of Jesus. I was interested in learning how widespread this perspective is.