Luke 1:17 "And he (John the Baptist) shall go before Him, in the spirit and power of Elias ..."
John the Baptist was not Elias, but he went in the spirit of Elias; as I understand it, he participated in the spiritual coming and role of Elias for the first coming of the Messiah, which was primarily spiritual in focus also. Elijah was there with John the Baptist in spirit, and he appears in Matthew 17:3, so that is why Jesus said that Elijah had already come, a requirement for the Messiah's coming. What they did to John the Baptist, they did in representative form to Elijah. For the full coming of the Messiah, which will fulfill all of the physical aspects of Messiah's work, Elijah will come physically.
The problems with the ancient (perhaps archaic) interpretations are compounded by traditional Old Testament understanding that require Elijah to preceed the messiah... the Suffering Messiah...
... and the Eucharist.
Jews know that Elijah's Cup was on the Seder table.
If Jesus ignored it, that would be impossible.
If Jesus used it, that would be Eliajah, returned.
in fact Elijah might still be coming back physical. The Book of revelation talks about two prophets of the OT coming back to bring God judgement.