The history of the Dark Saber is not a straight line and even though it seems like it. It is not like the Elder Wand in Harry Potter which has a master who must obtain the Saber defeating its owner in combat.
These are the people who have processed the Dark Saber
- Tarre Vizsla: He is the original owner and builder of the Dark Saber. The only Mandalorian Jedi this was around 1032 BBY. It was taken from him and placed in the Jedi Temple
- Pre Vizsla: He and other members of Death Watch stole back around 21 BBY. He attempts to use it to reunite the Mandalore.
- Darth Maul: He killls Pre Vizsla and takes the Saber but he is defeated by Dark Sidious but he does not take the saber. Maul has it as late as BBY 19. He is eventually killed b Obwan but the Saber is long gone.
- Kanan Jarrus: In Rebels Sabine Wren gets the Saber from the Nightsisters and gives it to the only Jedi she knows which Kanan Jarrus.
- Sabine Wren: Kanan Jarrus gives it back to Sabine and tries to train her to use it.
- Bo-Katan Kryze: Sabine Wren then gives it to Bo-Katan so she can reunite Mandalore. She fails and the result is The Great Purge in during the Emperial Era. She flees and leaves the Saber.
- Moff Gideon: He was a general in the Purge and ends up with the Saber around 9 ABY.
- Din Djarin: Defeats Gideon and takes possession of the saber but offers it to Bo-Katan who refuses it because she had to win it in battle.
So when you look at the history the possession of the Dark Saber has really only moved from one owner to another via direct combat twice. The Saber has never united the Mandalorians it has almost always divided them. I think that is will do that again. Din Djarin is the owner of the Saber in the eyes of The Watch. They will not follow Bo-Katan if Din Djarin is still alive. She would be seen once again as a pretender.
The Mythosaur in the room is the other prophecy which The Armorer alludes to. That the return of the Mythosaur will be the start of the new era of Mandalore. It is not clear that Din Djarin saw it. Bo-Katan knows the old stories and prophecies. The Mythosaur is central to the Mando culture and is axiomatic. It is the origin point. It is older than the Dark Saber and one who can bring it back and maybe even "ride it" like their ancestors will trump the owner of the Dark Saber.
To me this is the conflict. She is not going to get the Dark Saber. DF & JF along with the director of Episode 2 Rachel Morrison make sure that you see that Din Djarin is still in possession of the Saber at the end of Episode 3. They zoom in on the Saber on his belt. I think he is going to retain the Saber and she will bring the Mythosaur and their factions will fight for control. The Dark Saber will once again be a source of division not unity. The question becomes who wins and in what manner. I believe that The Armorer has a hidden agenda. She knows more than she tells Mando and might be using him to meet her goals.
I agree 100% that the show took a huge leap towards what we want to see. He is my wild theory. Who in the show can both wield a lightsaber and control an animal? Grogu is the only one and he is a now both a Mandalorian Foundling and a Jedi.