What other explanations exist for this prophecy? What do other denominations think it means that Elijah will "turn the hearts of fathers to their children and the hearts of children to their fathers?"
The Bible teaches that the Spirit of Elijah would be sent to the earth a total of 5 times (5 is the number of grace1). By Spirit of Elijah, I mean God's spirit anointing a man to bring a message, in the same way that the first Elijah was anointed (a straight shooter, hard hitter, come out of the wilderness, etc).
First, Elijah Himself
An examination of Elijah's traits may be beyond the scope of this question. If requested, I can revisit later.
Second - Elisha
II Kings 2:9 And it came to pass, when they were gone over, that Elijah said unto Elisha, Ask what I shall do for thee, before I be taken away from thee. And Elisha said, I pray thee, let a double portion of thy spirit be upon me.
II Kings 2:15 And when the sons of the prophets which were to view at Jericho saw him, they said, The spirit of Elijah doth rest on Elisha. And they came to meet him, and bowed themselves to the ground before him.
Third - John the Baptist (Forerunner to Jesus' First Coming)
Malachi 3:1 Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts.
Luke 1:17 And he shall go before him in the spirit and power of Elias, 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.
Matthew 7:11-13 And Jesus answered and said unto them, Elias truly shall first come, and restore all things. But I say unto you, That Elias is come already, and they knew him not, but have done unto him whatsoever they listed. Likewise shall also the Son of man suffer of them. Then the disciples understood that he spake unto them of John the Baptist.
Fourth - Forerunner to Jesus' Second Coming
Reading Malachi 3 as referring to John the Baptist's fore-running of Jesus' first coming, Malachi 4 can be read as another fore-runner preparing the way for Jesus' second coming. This man will turn the hearts of the children (the believer's of today) to the original faith preached by the early church apostles (fathers), just as John turned the hearts of the fathers of Israel to the "children" that received his message of the coming Christ. Malachi 4:5 predicts that this messenger will come before the great and dreadful day of the Lord, and if his message is rejected, the earth will be smitten with a curse.
Luke 1:17 specifically states that John would turn the hearts of the fathers to the children (Jesus' first coming), but does not include the Malachi 4:5 reference to turning the hearts of the children to the fathers (Jesus' second coming). This is similar to how Jesus, in the synagogue, began to read from Isaiah 61:1-2, but stopped halfway through verse 2 before he got to "and the day of vengeance of our God". He would fulfill that part of that verse at his second coming, but not his first.
Fifth - One of the Two Witnesses to Israel
REVELATION 11:3 And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.
See my response to this related question: Who Are the Two Witnesses?
To briefly summarize that more detailed response, the characteristics of the two witnesses are so similar to Moses and Elijah that we can conclude that the anointing of the two witnesses will be the same that was with Moses and Elijah. This is the fifth and final time that the spirit and power of Elijah will be manifest on earth.
1 See EW Bullinger's Number in Scripture, on the number five.
You ask for what groups besides the LDS have alternate views on the meaning of this passage. There is group knows as Branhamists (or by their own internal name of Message Believers) who, like me, believe that the fourth Elijah mentioned in Malachi came to earth in the person of William Marrion Branham. Like the LDS, this is a reconstructionist faith and we believe the original apostolic faith of the Bible has been lost and a new prophet sent to restore it.
The return ministry of Elijah is according to the Bible. The ordained one will come in the Spirit of Elijah doing the same works of Elijah:
- does not compromise on the Word of God
- will stand alone if "he" has to
- will indict the generation for the second crucifixion of Jesus Christ
- will not be someone after money or popularity
- will forerun the coming WORD
- will reveal the anti Christ system "Mystery Babylon"
- above all he will have "thus saith the LORD"
You just described William Branham's Ministry. Unlike LDS and Islam, God's prophet won't have to write a separate Bible, the true messenger (Earthly angel) will turn the Heart's of the children back to the revealed word that's been misconstrued through Man's theology, just as the Pharisees had misconstrued the Old Testament of their day. But unlike Paul, John, and the Old Testament prophets that had an anointing to write the message of God, according to Revelation 10:7, this 7th angel, the 7th angel to the Laodiceans of Revelation 3, will have an anointing to speak the word, "In the days of the VOICE of the Seventh Angel". God told John to seal up those things and write them not in Revelation 10:4, but we come to the 7th verse He says, "BUT in the days of the VOICE of the 7th angel, when HE shall begin to sound, the mystery of God should be FINISHED, as He hath declared to His servants the Prophets". That word angel is translated as messenger. Another interesting note, the name Malachi means "Angel". Coincidence? Is anything in the Bible ever a coincidence? Then as soon as Revelation 10 is finished, Revelation 11 reveals that Moses and Elijah will witness to the JEWS, when the gospel has been turned from the Gentiles back to the Jews due to the Gentiles rejecting the Gospel. Whether they physically are Moses and Elijah, or spiritually, we have no authority to say, for God will reveal that in due time.