I find this extremely interesting, especially when we look at the Gospel of Matthew:Matthew 17: [2] And he was transfigured before them. And his face did shine as the sun: and his garments became white as snow. [3]
And behold there appeared to them Moses and Elias talking with him.
It would seem to me that the prophesy was indeed fulfilled. The Transfiguration happened very shortly before they went up to Jerusalem for the pasch. So, Elias did come to ‘announce’ that the Messiah had arrived. I know there are some who see John the Baptist as the ‘coming’ of Elias, but that never made much sense to me. For some reason, when I read that post it finally clicked. That was the reference to the return of Elias, connected with the Messiah. (I guess I’m a little slow on the uptake, sometimes.

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According to St. Matthew’s God-inspired testimony, Jesus Christ claimed that St. John the Baptist fulfilled the role of Elijah. It should be of interest that this declaration of Jesus came
after the Transfiguration in which Elijah appeared with Moses on the mountain with Jesus.
Matthew describes the conversation between Christ and his disciples as follows:
And the disciples asked him, “Then why do the scribes say that first Elijah must come?” He replied, “Elijah does come, and he is to restore all things; but I tell you that Elijah 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.” Then the disciples understood that
he was speaking to them of John the Baptist.—Matthew 17:10-13, italics added.
So according to Jesus, John the Baptist was “Elijah…already come.” They “did to him whatever they pleased” in that John was jailed and beheaded in prison. This did not occur to the vision appearance of Elijah, so Jesus could not be speaking of him.
Again it should also be noted that this statement of Jesus happened immediately *after *the Transfiguration. Not only would this have been the perfect time for Jesus to state that the literal Elijah had come in the person of the mountain vision, the Holy Spirit would not have failed to inspired St. Matthew to note this in his narrative. So there is a link a between the two, as you noted. It’s just that Jesus was quick to add that Elijah was not to literally return. Like the prophet Elisha that took up Elijah’s cloak after the original prophet had been taken up, the “cloak” or position of “Elijah” now came to a different person, namely John the Baptist.–See 2 Kings 2:6-14.
Jesus tells his disciples that the Transfiguration was a “vision,” not a literal historical visit to earth of Moses and Elijah (even though they were likely involved in its presentation from heaven). As a vision and not a corporeal reality, the vision of Moses and Elijah was limited to the audience selected by Christ, which is clear from the fact in that he allowed only Peter, James, and John to witness it and then forbade them to mention a word of it until after his Passion.
As they were coming down the mountain, Jesus commanded them, “Tell no one the
vision, until the Son of man is raised from the dead.”—Matthew 17:1-9, italics added.
Because it was a vision limited to a select audience, this visionary appearance of Elijah could not be a fulfillment. Elijah was to engage in a ministry that was interpreted as introducing the coming of the Messiah. Jews who do not believe this has occurred yet still pray for this event to occur which is evidence that a select-audience-only vision could never be considered as a fulfillment.–See also Malachi 3:1.
But it is a good guess and, if it were not for what Jesus said right after the Transfiguration may have been what others could have concluded based on the same line of reasoning you have presented here.