Well, time loops are quite common. A character might find themselves stuck in a loop where they keep reliving the same events over and over again until they figure out how to break it. This can add a lot of suspense and mystery to the fanfiction. Also, the discovery of new technologies through time travel is interesting. Maybe a character travels to the past and brings back knowledge that changes the course of the war against the Cylons in a way that no one could have predicted.
One interesting concept is the idea of changing key events in the original Battlestar Galactica storyline. For example, a character might travel back in time to prevent a certain battle from happening, which could have huge ramifications for the future of the human race in that fictional universe. Another concept could be characters from different time periods within the Battlestar Galactica world interacting in unexpected ways. It could lead to new alliances or rivalries that were not part of the original narrative.
In some Battlestar Galactica time travel fanfiction, an interesting concept is the moral and ethical dilemmas that time travel presents. For instance, if a character has the ability to change the past to save lives, but it might mean sacrificing the future in some way. Do they go ahead and do it? It makes for great character exploration. There are also concepts like alternate timelines, where the actions of the time traveler create a completely different version of the Battlestar Galactica universe, with different characters, relationships, and outcomes.
Some interesting concepts would be related to the cultures. The Spartan culture in Halo with its focus on combat and loyalty could interact in an exciting way with the more democratic and diverse culture of the colonies in Battlestar Galactica. Then there's the idea of the Halo's Forerunners' technology falling into the hands of the characters in Battlestar Galactica. It could change the power dynamics completely. Also, the Cylons' ability to infiltrate and the Covenant's religious fanaticism could create some really complex and engaging storylines when combined.
One interesting concept could be the different alien cultures and their hierarchies. For example, some fanfics might explore an alien species where females are the dominant gender in their society, which is a contrast to the human culture in Battlestar Galactica. Another concept could be the unique technologies of the aliens. Maybe they have a way of traveling through space that is far more advanced than the humans', like being able to open portals instead of using traditional FTL drives.
One interesting storyline could be a self - insert character who has unique knowledge about the Cylons' weaknesses and uses it to help the Galactica crew. For example, they might know a way to disrupt the Cylons' communication network that was never discovered in the original series.
One idea could be exploring the backstories of minor characters in more depth. For example, the lives of the pilots who don't get as much screen time. Another could be a what - if scenario where a different character discovers the Cylons' plan earlier. And a third could be a story about a new colony that is formed during the journey through space.
Admiral Adama is often a popular character in these fanfictions. His leadership qualities and strategic mind make him a key figure in any time - travel related plot. He could be the one making decisions about how to use time travel to the advantage of the fleet.
One interesting crossover could be the use of Destiny's weaponry in the Battlestar Galactica universe. For example, Guardians from Destiny could bring their advanced energy guns to help the crew of the Galactica in their fight against the Cylons. This would change the power dynamics in the BSG battles.
One idea could be the Stargate teams finding a derelict Battlestar and trying to figure out its technology. They might encounter some of the Cylon technology which could pose a new threat or a source of new knowledge for them.
A possible fanfiction plot could involve a character from Battlestar Galactica having some latent magical ability. This person discovers the world of Harry Potter through a strange portal or something. They then have to learn how to use their magic while also trying to bring some of the magical solutions back to help their own people in the fight against the Cylons. And perhaps there could be a conflict between the magic - using wizards and the technology - reliant Galactica crew at first, but then they learn to work together.
The secrets of the Battlestar Galactica shipyards in fanfiction can be quite diverse. It could be that the shipyards are actually a front for something else entirely. Maybe they are secretly researching ways to communicate with other civilizations that are not supposed to be known. There could also be a hidden level in the shipyards where captured enemy technology is being reverse - engineered. Also, there might be a select group of people who know about a special power source that is being harnessed in the shipyards, which could potentially change the balance of power in the Galactica world.
One great fanfiction could be about a crossover between the two universes. For example, a story where the technology of Stargate is combined with the spacefaring capabilities of Battlestar Galactica. Maybe the characters from both have to work together to fight a common enemy like a powerful alien race that is threatening both their galaxies.