After the transfiguration Jesus’s disciples asked Him about the coming of Elijah.  This is recorded in both Matthew and Mark.

Mat 17:10  And His disciples asked Him, saying, “Why then do the scribes say that Elijah must come first?“
Mat 17:11  Jesus answered and said to them, “Indeed, Elijah is coming first and will restore all things.
Mat 17:12  But I say to you that Elijah has come already, and they did not know him but did to him whatever they wished. Likewise the Son of Man is also about to suffer at their hands.”
Mat 17:13  Then the disciples understood that He spoke to them of John the Baptist.

Mar 9:11  And they asked Him, saying, “Why do the scribes say that Elijah must come first?“
Mar 9:12  Then He answered and told them, “Indeed, Elijah is coming first and restores all things. And how is it written concerning the Son of Man, that He must suffer many things and be treated with contempt?
Mar 9:13  But I say to you that Elijah has also come, and they did to him whatever they wished, as it is written of him.”

The interesting phrase is, “Elijah is coming first and will restore all things”. 

There are two main ways of understanding this. 

One, is that it refers solely to John the Baptist.  This is indicated by Mat 17:13, “the disciples understood that He spoke to them of John the Baptist”.  The restoration of “all things” must be understood as “all manner of things”.  This is certainly legitimate as the Greek word translated “all things” is pas, that can mean, “all, any, every, all manner of”. 

The other, is that the phrase “Elijah is coming first and will restore all things”, refers to an end time Elijah to come who will “restore all things” before the second coming of Jesus Christ. 

Before discussing this further it is instructive to review all the Scriptures pertaining to the coming of Elijah.

Malachi prophesied of a messenger who God would send to prepare the way of the coming of Jesus Christ.

Mal 3:1  “Behold, I send My messenger, And he will prepare the way before Me. And the Lord, whom you seek, Will suddenly come to His temple, Even the Messenger of the covenant, In whom you delight. Behold, He is coming,” Says the LORD of hosts.

The gospel writers quote this when explaining that John the Baptist fulfilled this prophecy.

Mat 11:10  For this is he [John the Baptist] of whom it is written: ‘BEHOLD, I SEND MY MESSENGER BEFORE YOUR FACE, WHO WILL PREPARE YOUR WAY BEFORE YOU.’

Mar 1:2  As it is written in the Prophets: “BEHOLD, I SEND MY MESSENGER BEFORE YOUR FACE, WHO WILL PREPARE YOUR WAY BEFORE YOU.”
Mar 1:3  “THE VOICE OF ONE CRYING IN THE WILDERNESS: ‘PREPARE THE WAY OF THE LORD; MAKE HIS PATHS STRAIGHT.'”
Mar 1:4  John came baptizing in the wilderness and preaching a baptism of repentance for the remission of sins.

Luk 7:26  But what did you go out to see? A prophet? Yes, I say to you, and more than a prophet.
Luk 7:27  This is he [John the Baptist] of whom it is written: ‘BEHOLD, I SEND MY MESSENGER BEFORE YOUR FACE, WHO WILL PREPARE YOUR WAY BEFORE YOU.’

There could also be an end time fulfilment of this but there is nothing specific to indicate it.  However,

Malachi also prophesied of God sending an Elijah before “the great and dreadful day of the LORD”, which is a reference to the end time.

Mal 4:5  Behold, I will send you Elijah the prophet Before the coming of the great and dreadful day of the LORD.
Mal 4:6  And he will turn The hearts of the fathers to the children, And the hearts of the children to their fathers, Lest I come and strike the earth with a curse.

The angel who appeared to Zacharias, the father of John the Baptist, quoted Mal 4:6.

Luk 1:16  And he [John the Baptist] will turn many of the children of Israel to the Lord their God.
Luk 1:17  He will also go before Him in the spirit and power of Elijah, ‘TO TURN THE HEARTS OF THE FATHERS TO THE CHILDREN,’ and the disobedient to the wisdom of the just, to make ready a people prepared for the Lord.”

This reference to the end time adds weight to there being an end time Elijah.

Interestingly, by comparing the phrase that follows, it can be argued that the meaning of turning “the hearts of the children to their fathers”, is turning “the disobedient to the wisdom of the just”. 

Moving on, Isaiah prophesied of a messenger preparing the way of Jesus Christ coming.

Isa 40:3  The voice of one crying in the wilderness: “Prepare the way of the LORD; Make straight in the desert A highway for our God.
Isa 40:4  Every valley shall be exalted And every mountain and hill brought low; The crooked places shall be made straight And the rough places smooth;
Isa 40:5  The glory of the LORD shall be revealed, And all flesh shall see it together; For the mouth of the LORD has spoken.”

The gospel writers quote this when explaining that John the Baptist fulfilled this prophecy.

Mat 3:1  In those days John the Baptist came preaching in the wilderness of Judea,
Mat 3:2  and saying, “Repent, for the kingdom of heaven is at hand!”
Mat 3:3  For this is he who was spoken of by the prophet Isaiah, saying: “THE VOICE OF ONE CRYING IN THE WILDERNESS: ‘PREPARE THE WAY OF THE LORD; MAKE HIS PATHS STRAIGHT.’ “

Luk 3:3  And he [John the Baptist] went into all the region around the Jordan, preaching a baptism of repentance for the remission of sins,
Luk 3:4  as it is written in the book of the words of Isaiah the prophet, saying: “THE VOICE OF ONE CRYING IN THE WILDERNESS: ‘PREPARE THE WAY OF THE LORD; MAKE HIS PATHS STRAIGHT.
Luk 3:5  EVERY VALLEY SHALL BE FILLED AND EVERY MOUNTAIN AND HILL BROUGHT LOW; THE CROOKED PLACES SHALL BE MADE STRAIGHT AND THE ROUGH WAYS SMOOTH;
Luk 3:6  AND ALL FLESH SHALL SEE THE SALVATION OF GOD.’ “

Joh 1:23  He [John the Baptist] said: “I am ‘THE VOICE OF ONE CRYING IN THE WILDERNESS: “MAKE STRAIGHT THE WAY OF THE LORD,” ‘ as the prophet Isaiah said.”

Zacharias, the father of John the Baptist, also prophesied that John the Baptist would prepare the way of Jesus Christ.

Luk 1:76  “And you [John the Baptist], child, will be called the prophet of the Highest; For you will go before the face of the Lord to prepare His ways,
Luk 1:77  To give knowledge of salvation to His people By the remission of their sins,

Clearly, John the Baptist fulfilled the prophecy about preparing the way of the Lord in Isa 40:3.  However, Isa 40:4-5, although quoted by Luke in Luk 3:5-6, was not fulfilled during the time of John the Baptist.  It is clearly a future event associated with the second coming of Jesus Christ.  This adds weight to there being an end time Elijah.

Let’s summarise the evidence is there for an end time Elijah.

Firstly, there is the reference to the end time in Mal 4:5.  If this refers only to John the Baptist then why the reference to the end time which is 2000 years later?

Mal 4:5  Behold, I will send you Elijah the prophet Before the coming of the great and dreadful day of the LORD.

Secondly, there is also Isa 40:4-5 which has not been fulfilled which is clearly associated with John the Baptist (who is a type of Elijah).

Isa 40:4  Every valley shall be exalted And every mountain and hill brought low; The crooked places shall be made straight And the rough places smooth;
Isa 40:5  The glory of the LORD shall be revealed, And all flesh shall see it together; For the mouth of the LORD has spoken.”

Conclusion

Is there an end time Elijah to come?  Based on Mal 4:5 and Isa 40:4-5, it certainly looks like it.