Quick answer: It may be a future creation...
I've read the Leviathan chapter many times. Its something hugely interesting to me.
Consider this seemingly unrelated scripture:
Psalm 139:16 Your eyes saw my unformed substance, and in Your book all the days [of my life] were written before ever they took shape,
when as yet there was none of them.
On this principle we might say that God is speaking of a Creature that does indeed exist to him, but not yet created (ie, some future creation). Just as God foretold the existence of humans in writing (and indeed has us all in writing ahead of time) it might be also true of this creature.
Every creature listed prior to the Behemoth and Leviathan were literal. It hardly makes sense that a sudden shift to the metaphorical would be made, as a comparison to the power of it's creator. (Job 41:10)
Compare Genesis 9:2 to Job 41. Job 41 does not describe a creature consistent with the statement:
"And the fear of you and the dread and terror of you shall be upon every beast of the land, every bird of the air, all that creeps upon
the ground, and upon all the fish of the sea; they are delivered into
your hand.".
If this creature existed during the time of Noah onnward, then this promise would be a lie. Of course, we know God doesn't lie. It seems likely (based on below proof) this is a future creation for a time when it will be most appreciated (and needed). It would possibly be under a different covenant / agreement than Noah or the one we are under.
Please note: I like quoting the amplified bible, but please mentally overlook references to "crocodile" in this excerpt.
JOB 41:
Can you draw out the leviathan (the crocodile) with a fishhook? Or
press down his tongue with a cord?
2 Can you put a rope into his nose? Or pierce his jaw through with a hook or a spike?
3 Will he make many supplications to you [begging to be spared]? Will he speak soft words to you [to coax you to treat him kindly]?
Sounds like it would make a great fish story! "I caught something THIS big!". Already we see a challenge in the writing. Do you dare...?
4 Will he make a covenant with you to take him for your servant
forever?
5 Will you play with [the crocodile] as with a bird? Or will you put him on a leash for your maidens?
Obviously implying that it cannot be tamed, like other creatures.
6 Will traders bargain over him? Will they divide him up among the
merchants?
7 Can you fill his skin with harpoons? Or his head with fishing spears?
Obviously implying it cannot be hunted and sold like other creatures.
8 Lay your hand upon him! Remember your battle with him; you will not
do [such an ill-advised thing] again!
One of my favorite verses. The bible's way of saying "You'll get your @$$ kicked by this thing." But seriously, its obviously made to be a testimony to how weak humans are in comparison to God's creations.
9 Behold, the hope of [his assailant] is disappointed; one is cast
down even at the sight of him!
Are we being metaphorical? We see a FUTURE prediction here."Behold, the hope of [his assailant] is disappointed; one is cast down even at the sight of him!" Likewise, we can deduce that nobody has seen him, based on this verse. Otherwise the explanation would not be needed.
10 No one is so fierce [and foolhardy] that he dares to stir up [the
crocodile]; who then is he who can stand before Me [the beast’s
Creator, or dares to contend with Me]?
11 Who has first given to Me, that I should repay him? Whatever is
under the whole heavens is Mine. [Therefore, who can have a claim
against God, God Who made the unmastered crocodile?]
This is an important verse. While this is commonly believed to be a crocodile, I could easily take one down even with a handheld weapon. If this were a crocodile or some creation we are accustomed to dominating, then verse 10 would be a very weak comparison of "who then is he who can stand before Me". Literally, this might be a very unique creature made to humble humans, quite possibly a future creature during a future time of judgement.
12 I will not keep silence concerning his limbs, nor his mighty
strength, nor his goodly frame.>
13 Who can strip off [the crocodile’s] outer garment? [Who can
penetrate his double coat of mail?] Who shall come within his jaws?
14 Who can open the doors of his [lipless] mouth? His [extended jaws and bare] teeth are terrible round about.
15 His scales are [the crocodile’s] pride, [for his back is made of rows of shields] shut up together [as with] a tight seal;
16 One is so near to another that no air can come between them.
17 They are joined one to another; they stick together so that they cannot be separated.
Do we assume something that exists, or a much bigger version of something that exists? Its possible this might be a highly altered version of a crocodile, or something resembling it in many ways. The next few verses invalidate the idea of a cold-blooded creature anyway.
18 His sneezings flash forth light, and his eyes are like the
[reddish] eyelids of the dawn.
19 Out of his mouth go burning torches, [and] sparks of fire leap out.
20 Out of his nostrils goes forth smoke, as out of a seething pot over a fire of rushes.
21 His breath kindles coals, and a flame goes forth from his mouth.
Definitely not a crocodile. Now we are in "Dragon" description.
22 In [the crocodile’s] neck abides strength, and terror dances before
him.
23 The folds of his flesh cleave together; they are firm upon him, and they cannot shake [when he moves].
24 His heart is as firm as a stone, indeed, as solid as a nether millstone.
25 When [the crocodile] raises himself up, the mighty are afraid; because of terror and the crashing they are beside themselves.
Again, not a creation we presently see, and yet we know that a mythical creature would not be used to testify to God's literal power as the creator.
26 Even if one strikes at him with the sword, it cannot get any hold,
nor does the spear, the dart, or the javelin.
27 He counts iron as straw and bronze as rotten wood.
28 The arrow cannot make [the crocodile] flee; slingstones are treated by him as stubble.
29 Clubs [also] are counted as stubble; he laughs at the rushing and the rattling of the javelin.
Notice we speak of weapons, but its really creation against creation. We are speaking of man and his inventions standing against a very powerful invention of the Creator. Its obviously created to humble people.
30 His underparts are like sharp pieces of broken pottery; he spreads
[grooves like] a threshing sledge upon the mire.
31 He makes the deep boil like a pot; he makes the sea like a [foaming] pot of ointment.
32 [His swift darting] makes a shining track behind him; one would think the deep to be hoary [with foam].
33 Upon earth there is not [the crocodile’s] equal, a creature made without fear and he behaves fearlessly.
So here we see God praising the power of this creation of his. For a creature to heat up water, and to leave a shining trail (and judging by references to it's lightning and fire breathing), this would have to be a very unique and special project, something holding many properties we often utilize for our own boastful little inventions: Electricity, combustion, etc. The words "Upon the earth there is not it's equal" verify that.
34 He looks all mighty [beasts of prey] in the face [without terror];
he is monarch over all the sons of pride. [And now, Job, [a]who are
you who dares not arouse the unmastered crocodile, yet who dares
resist Me, the beast’s Creator, to My face? Everything under the
heavens is Mine; therefore, who can have a claim against God?]
Again, a mythical beast to make a literal point? If it were pretend, it would be meaningless as a testimony to the literal power of the creator. This creature is obviously made (or will be made) as a means of humbling.
In conclusion
Many believe in a future resurrection of people to flesh, a time of judgment, to separate the good from the bad (entirely different subject). There are probably different spans of time (ages) in which different groups of people and possibly creations are brought back to existence for a first and second time.
I've always considered this passage to be an exceptional one, something to look forward to. While I certainly don't have any hunter's instinct, I'd love to see this thing from a safe distance one day!