There are two lenses through which one can analyze the current state of 3D Platformers, a.k.a. 3D Character action games. And by pedantically needing to point out that distinction, I'm already revealing the dichotomy I plan to talk about.
First, the lens of the 3D platformer. Through this lens, it seems that there is a once-popular genre known as the 3D platform game, which is characterized by cute characters hopping their way though colorful worlds. To people who see the landscape of games through this lens, there's currently a revival of 3D platform games. The theory being that, after the boom in the 5th console generation (PS1, N64, Sega Saturn) 3D platform games were supplanted by action games like Grand Theft Auto, Call of Duty, and Assassin's Creed. And now, years later, a groundswell of nostalgia has demanded their return.
On the other hand we have the lens of the Character Action Game, through which we see an unbroken lineage of games going from Super Mario Brothers all the way to Assassin's Creed Origins.
After Jason Rubin left Naughty Dog, that company went on to make Uncharted. Although Rubin had never seen Uncharted prior to its release, when he saw it, he saw it as the completion of the mission he'd first set for Naughty Dog when he helped found it. Uncharted was the achievement of all the goals he'd originally set for Crash Bandicoot (a character action game with mass-market appeal and interwoven story).
Through the lens of the character action game, we also see the successful parkour and combat from Prince of Persia were refocused into Assassin's Creed. Ratchet and Clank is the game that Spyro had been desperately trying to be for two consecutive sequels. This all being corroborated by stories from the developers themselves.
The point being that the 3D character action game never disappeared. The form of a 3D CAG is simply dependent on the times. In particular, they have been shaped by two counteractive trends, the first being combat.
In modern CAG's, heavy demands are placed on the player in terms of fending off enemies. Compare Crash Bandicoot 2's enemy interactions with Assassin's Creed's. Crash's combat consists of one hit kills, two types of attacks, and some enemies which are only vulnerable to one of them. By contrast, Assassin's Creed games now have a large offering of weapons, many with several combat moves per weapon. There are various gameplay states which change the mode of combat. There are combo moves, defensive moves, items for stealthy escapes, etc.
The second trend is movement. You might think that being more movement based, older character action games would have more sophisticated movesets. But upon examination, the opposite is true. In order to navigate his environment, Spyro the Dragon may walk, charge, jump, and glide. In Uncharted, Nathan Drake can walk, run, jump, leap to ledges, shimmy along them, drop down onto a ledge, walk on tightrope-like objects, climb, pull himself up a ledge, climb and jump between ladders and poles, and on and on and on.
I said these trends were counteractive, and here's what I mean. There is a limit to how many controls a game can teach a player. At least a mass-market game. These games were succeeding by making combat a focus, and by making the character move in exciting ways. So they had to make a choice. And invariably, they chose to make the movement mechanics more and more guided, and the combat mechanics more and more demanding. By the time we reach Assassin's Creed III, the movement is all but automatic. The move sets are now incredibly complex but it is the game which is now making the moves, not the player. It's an elegant resolution to the contradictory needs of a sophisticated navigational moveset and complex, demanding combat.
Because I subscribe to this second lens, the lens of the CAG, which says that '3D platformers' never disappeared, my take on their current 'revival' is this:
Games enthusiasts have a sense that there's something missing from the games they're playing now, and they have a vague sense that the last time they had the thing which is now missing was around 2003. This thing might be a focused offering of mechanics, or art that was trying to look like Saturday morning cartoons rather than an action film.
But the typical consumer does not have the insight to see what it is particularly that they miss about the dawn of 3D. So they clamor for everything they think they remember about them. And game developers have been happy to oblige, much to consumers' disappointment. Lacking insight, they say that the new '3D platformers' made to their exact specifications are too difficult, the level-design too opaque, the difficulty too punishing.
The irony here is that you can't make a game like Spyro the Dragon or Crash Bandicoot by letting consumers dictate the design, because the methodology in which those games were made specifically prohibits letting consumers dictate the design of your game, advising instead to pay attention to body language and facial expression.
So as I find myself making a "3D platformer," in a way I'm trying to imagine an alternate timeline, in which combat disappeared from CAG's altogether, and in which the move set remained consistent and firmly in control of the player. I think it's all but inevitable that the world will label my game a 3D platformer, but I'll be trying like hell to make a CAG.