Since there's no legitimate confirmation of Assassin's Creed Ragnarok, most rumors should be taken with a grain of salt. Where and when it is set, if the protagonist is named Jora, and several of the rumored mechanics like co-op are all just that, rumor. However, if there's anything known for sure about the game, the fan-titled Assassin's Creed Ragnarok is indeed about Vikings. High-profile corroborations and teases straight from Ubisoft tell fans this much.
At first, it seems like a strange concept to mold Vikings and Assassins, but it's worth mentioning that the Viking Era takes place before the first game. Characters in Assassin's Creed Ragnarok wouldn't be members of the Brotherhood, per se, and would instead be Hidden Ones, Bayek's original organization. Origins isn't the only game that has lore to help shape and contextualize a Viking-Assassin world, as the idea has existed in-universe since 2014's Assassin's Creed Rogue.
Assassin's Creed Ragnarok: Shay Patrick Cormac
Most Assassins are connected somehow, mostly through Desmond Miles as ancestors. One who sticks out like a sore thumb intentionally is Shay Patrick Cormac, an Assassin-turned-Templar in Colonial America who was born to Irish immigrants. Considering the map of Assassin's Creed Ragnarok ostensibly includes Ireland, as Viking raids did occur there, it's well-within reason that Ragnarok's purported protagonist Jora could be an ancestor to Cormac.
Cormac's Templar outfit echoes this same idea. It's adorned with Celtic knots, Yggdrasil, and triquetras, all of which are loosely connected to Vikings. Celtic Knots are less so, yet are tied to the region of Ireland. Norse and Celtic people are known for their Knotwork, so it's not a stretch to associate the two. Yggdrasil is a great tree derived directly from Norse mythology, and as such, is a direct connection between the two. AC Odyssey explored Greek myth thoroughly, even more so than AC Origins did Egyptian, and so with this emphasis, it's possible that Yggdrasil and the Norse Gods play some role in the upcoming game.
A Triquetra is often depicted in various cultures, and in the Norse world, it was often associated with Mjolnir and the like. Reportedly, one of Assassin's Creed Ragnarok's special editions would include a version of Mjolnir, so its inclusion here could have been some foreshadowing. A Triquetra symbolizes three things, and combined with Cormac's symbolism, could have been meant to foreshadow an eventual Viking game anyhow.
Assassin's Creed Ragnaok: Otso Berg
If Cormac's symbolism is a subtle hint for Assassin's Creed Ragnarok, then Otso Berg is practically screaming it. The two characters have always been similar in that particular game down to the design details, and it's clear by the ending of the Fate of Atlantis DLC that the character may be important in the next game, which practically screams the viking connection.
It's revealed at one point that Otso Berg has a Viking ancestor who took part in the Lindisfarne raid in 793 AD. This lines up perfectly with the rumored time period of the next game and provides in-game context, but it also paints an interesting picture. This Viking defeated a Saxon warrior, offered him a chance to join the clan, and upon being refused, killed him mercilessly. It's possible that Otso Berg's ancestor is part of the same clan as the player character, if not more interesting THE player character, but all will be revealed in due time. What's clear is the open ocean of rumors is that it's about Vikings, and Ubisoft has been setting it up since Assassin's Creed Rogue.
Assassin's Creed Ragnarok is out now for PC, PS4, and Xbox One.