While Loki was the first Disney Plus series that spent as much time as it did on time travel and the multiverse in the MCU, there are plenty of comic storylines that have some sort of journeys between the past and the future. While Marvel doesn't mess with the timeline in its comics as much as DC does with stories like "Flashpoint" it's obvious that there are more than a few time travelers, considering that's exactly where Kang the Conquerer came from. He's hardly the only time traveler in the comics. There are actually quite a few that would make perfect sense to eventually join Loki Season 2.
One of the unlikeliest of time travelers in the Marvel Comics universe is that of the Ghost Rider. In actuality, the character was the Cosmic Ghost Rider which was actually Frank Castle, otherwise known as the Punisher who managed to become possessed by the Ghost Rider entity as well as a cosmic power that had the ability to time travel. The backstory of Cosmic Ghost Rider is actually pretty convoluted and it would seem as though the Disney Plus version of the character might not have the entire backstory as it did in the comics, but the character popping up in some fashion makes quite a bit of sense.
Right at the top of the list of why some kind of time-traveling Ghost Rider makes sense is because there have been rumors for quite a while now that Disney and Marvel want to find a way to bring the character back. While the most prominent rumors are a Ghost Rider movie, the character could first make an appearance on the streaming platform. Should the rumors that Norman Reedus is going to play the character it would make even more sense. He's someone who will soon have a little more time on his hands with the end of The Walking Dead and he's a well know TV actor. Quite frankly it makes a little too much sense to bring this character in some way, shape or form to Loki Season 2.
Speaking of characters that just make way too much sense for Loki Season 2, there's Iron Lad. For those who aren't aware, Iron Lad is one of the Young Avengers and he does indeed look a bit like Iron Man, though his "helmet" is actually his head and face. He was quite a powerful hero, until he became quite the powerful villain. In fact, he eventually became one of the most deadly villains the Avengers ever faced off against. Iron Lad actually goes on to become none other than Kang the Conqueror. Considering that Season 1 Kang talked about multiple versions of him all coming, it seems extremely likely that one of them will be Iron Lad. In fact, this particular character has been guessed at before. There was even some talk that he might make an appearance in Season 1 but that never came to be. It seems likely the Disney Plus series will fix that in the next installment.
There are two very big reasons why Victor Von Doom feels like a no-brainer when it comes to characters that could make an appearance in Loki Season 2. The first is that there have been all kinds of rumors that a Fantastic Four movie is going to be coming to the MCU at some point. Much like the potential appearance of Ghost Rider as a way to introduce the MCU version and then lead into his own movie, the same could be said of Doctor Doom. Why the well known villain from the Fantastic Four instead of one of the heroes? That's the other reason why the character makes quite a bit of sense for the series.
Doctor Doom actually has a long history of time travel in the Marvel Comics. He created something called the time platform that he often uses to go on raids to grow his wealth. However, the time platform is even more important than that. It was using this device that members of the Fantastic Four first ran across Kang the Conqueror. The dual use of Doctor Doom in this storyline just seems like it would come in handy a bit too easily.
Much like Doctor Doom, not only does Kitty Pryde make some sense when it comes to joining Loki Season 2 because she's done the time-traveling thing, but because it would be an excellent way to introduce her character and that of the X-Men into the MCU. There has been lots of talk about that group of super-powered people joining the Marvel Cinematic Universe at some point in the very near future.
Kitty could also be someone who could be used to introduce the concept of the X-Men while not having to introduce more than her character, as she's someone who time travels by herself. Usually, her powers allow her to phase through solid objects, but at one point she also figured out how to basically send her consciousness through time and space. She could basically be a soft launch of the X-Men on Disney Plus.
If Marvel and Disney Plus don't want to introduce a whole new group of people, then there's still at least one more character that could be brought into the show, and have it be based on existing MCU personalities. Nadia Van Dyne is actually the daughter that no one knew Hank Pym had for quite a while. Or at least they thought she was dead for quite a while. She eventually became a different version of the Wasp in Marvel Comics. The character had a couple of different run-ins over the years with time travelers and Kang himself and it doesn't seem like it would be hard to include this character in Loki Season 2.
In fact, with the alternate realities that are already an established pattern in the MCU thanks to End Game and Loki, Nadia Van Dyne could actually just be a different Hope Van Dyne so the showrunners wouldn't even have to work that hard to create the character. There's already a tie-in to Ant-Man and the Wasp with Loki and Kang, so it's possible this could be yet another way to introduce a character that will eventually appear on the big screen.