We all know Natalie Portman will reprise her role as Jane Foster in Thor: Love and Thunder, after Thor: The Dark World. But MCU isn't bringing her back just to make up with the Thor and be her weak human Girlfriend, this time she will become the Lady Thor.
There's A New Thor In The Market
How would she become worthy of the Hammer when there's no hammer at all, as it was destroyed by Thor's sister. This could only be solved by introducing Lady Thor from a different universe, but it just doesn't fit right to put "alternate world" as the reason behind everything.
But Mjolnir Is Already Destroyed
This way MCU will just introduce anyone anyhow just by placing a tag of different Universe, MCU will ruin its own Universe, we need logical reasoning behind Jane becoming Thor, like in the Comics.
MCU Can't Be This Stupid
Thor 4 may also lead to a new Avengers 5 team, since there's no one to lead after Tony and Captain's death, and there are too many heroes in the same universe, in the same country itself, it's a difficult choice for MCU to put one hero in Avengers and exclude others.
Beginning Of The Avengers 5
The main antagonist 'Gorr: The God Butcher' will definitely kill a hero before getting killed, given his reputation of butchering the gods. Gorr is meant to be the deadliest enemy the Thor will face, deadlier than her sister Hela: God Of Death herself.
Death Is Certain
Bringing only the Mjolnir from another universe will be fine & then Jane Foster becomes worthy of wielding it to destroy The God Butcher along side Storm breaker wielder Thor, It looks logical as it would take more than one Thor to defeat the god butcher but bringing Mjolnir from alternate world still shows lack of creativeness.
Hammer Problem Ain't Solved Yet
The Giant Dwarf isn't dead of course but reforging the Mjolnir is not enough as anyone could lift it, unless Odin spells his words into it and makes it a requirement to become worthy of it to even move it an inch, but... 'He is Dead'... So it's absolutely nuts how MCU will pull this off.
Can't The Gaint Dwarf Forge It Again?
Though there's a new character just like Odin but from a different origin, The Zeus from Greek. It's confirmed that MCU will introduce Zeus and fans are very curious on how MCU is planning to mix up Norse & Greek Gods together, and yeah also an Egyptian God which created "The Moon Knight" in the first place.
True God / False God
MCU has promised to launch like a thousand new projects and literally turning into a Universe of its own, but the only thing crucial here is to not introduce anything as 'from alternate world' for which they can't find any logical creative origin story without loopholes.
MCU Mustn't Turn Into Cartoon Network