Fate of Elves and Ents

The result would be the final straw that pushes the elves out of Middle Earth. Granted, the process of them leaving had been ongoing since prior to the awakening of men. But now there is literally nothing holding them back. Morgoth was defeated in previous ages, who was the motivation for many of the elves returning to or staying in Middle Earth. By the end of the War of the Ring, Sauron, the last dragons and balrogs were defeated. Orcs were effectively eliminated as a major threat. Which means that not just Morgoth but all of his influence was now gone too. Essentially, this means that the broadest interpretation of historic mission can now be said to be accomplished.
On the other hand, the Blue Wizards are potentially causing problems. At the very least one of them took power for themselves, even if they do not turn that power against the rest of Middle Earth. Aragorn appears to be turning more authoritarian as time goes on. Chaos in the post Sauron era and the rise of industrialization would mean that the fighting and environmental damage continues. Even with their historic mission accomplished, there would be a sense that it meant little. The elves would be justified in feeling that Middle Earth is a bit of a lost cause. No matter what they do, no matter how much they try, nature suffers and fighting rages on.
And with such a conclusion they will leave. The seeming total abandonment of Lothlorien by the end of Aragorn's reign is not a shock. Mirkwood would probably be similarly quick to lose its elven population. Mirkwood was the most devastated elven realm and Galadriel's ring amplified her desire to leave. Because Rivendell is a solid transit point and elven, it would probably remain populated for longer. But not by much. Once this role of helping migrants cross the Misty Mountains has been filled, it too will enter terminal decline. Lindon is the last stop before the undying lands. As such it will struggle on for longer and for similar reasons to Rivendell. But its days will come to an end too.
The ents would not fare too well either. Industrialization would fuel the need for wood. The previous destruction of the entwives means that they are nearing the end of their existence as a species. It is entirely possible that a war will break out between the ents and Gondor as Gondor industrializes. But this would simply speed up the process. The ents effectively just defend Fanghorn. But as elven influence declines, the great reserves of Mirkwood and Lothlorien would be available to Gondor.
Ents do have powerful advantages in open battle. So initial losses would probably be great. But the use of star fort elements developed in Isengard and new weapons would negate these. The role of living artillery is the ent's primary one. But star forts are designed specifically to counter improved artillery. Gondor's new cannons would also be one of the more effective tools against the ents. Traditional medieval weapons would not do much. But a large and fast moving iron ball would at least knock over an ent and likely do significant damage. Which then makes the traditional armies much more effective.
All told, the ents would lose in a low intensity conflict. Their just war posture would lead them to conflicts as industrialization progresses. And each fight would do a lot of damage to both sides. But Gondor would learn from each fight and the ents cannot replace their losses. Ironically, their victorious war against Isengard would lead to Isengard destroying them.
With the last defense against deforestation is removed, massive changes will occur in Gondor. Most obviously, industrialization now can progress unchecked. But more important is the return of Gondor's navy. One of the main reasons the old forests of Middle Earth no longer exists was the demand for wood to build Gondor's navy. With no real checks on its military power and increase in coastline, rebuilding the navy makes sense. Which would then see Gondor become a naval power again.
Aragorn would probably be keen on doing this too, as it helps him solidify his power over the Umbar area. Trade with Harad becomes more secure with a fleet too. As does the defense of the Southern Fiefs. Transporting troops, goods and messages to Arnor is facilitated as well. Lastly, there is the symbolic importance. The kin-strife is what led to the loss of Umbar and Gondor's original navy, created the Corsair threat and signalled the long decline of Gondor. Through the naval rearmament program, Aragorn can signal his rule reverses the entirety of Gondor's dark ages.