Yes, there are likely 'Bardock Kills Frieza' fanfics out there. The Dragon Ball universe has a huge fan base, and many fans like to create alternative storylines. You can try searching on fanfic websites like FanFiction.net or Archive of Our Own.
Family dynamics is another. As brothers, their relationship can be complex. Some fanfics show loyalty between them, while others highlight jealousy or rivalry. For example, a fanfic might explore how Frieza's jealousy of Cooler's strength affects their relationship.
One great 'Frieza fanfic' is 'The Redemption of Frieza'. It explores a different side of Frieza where he has a chance at redemption. Another is 'Frieza's New Empire' which shows Frieza building his power in a new and unexpected way. And 'Frieza and the Time Rift' is also interesting as it involves Frieza getting caught in a time - traveling adventure.
The combination of Frieza, a character from a very different universe, with the RWBY setting makes it unique. RWBY has its own set of rules, powers, and characters. When you introduce Frieza, who has his own brand of power and villainy, it creates a whole new dynamic. For example, his ability to transform and his extreme power level contrast with the more gradually developed powers in RWBY.
There's a fanfic where Frieza arrives in the RWBY world and tries to take over. He starts by sizing up the Huntsmen and Huntresses as potential threats or pawns. In this fic, the author does a great job of showing how Frieza's cold and calculating nature clashes with the more idealistic characters in RWBY. It's a really engaging read if you like that sort of crossover concept.
Then, introduce some shared experiences. Maybe they get trapped in a strange dimension together. In this new and dangerous place, they have to rely on each other's strengths. Goku's physical power and Frieza's cunning could be the keys to their survival. As they go through these experiences, they start to see each other in a new light and their relationship begins to change.
The plot could start with Bardock having a premonition of Frieza's future actions against the Saiyans even before the destruction of Planet Vegeta. He then secretly trains and discovers a new form or power that allows him to stand up to Frieza. When Frieza arrives to destroy the Saiyans, Bardock reveals his newfound strength and battles Frieza. After a long and intense fight, Bardock manages to defeat and kill Frieza, changing the course of the Dragon Ball universe. This could also lead to new alliances and power struggles among the remaining characters.
One common theme is redemption. Frieza is often portrayed as having a chance at redemption through his interactions with Goku. For example, in some fanfics, Goku's unwavering belief in the good in people (or in Frieza's case, beings) starts to make Frieza question his own evil ways.
A plotline could start with Frieza hearing about Broly's power and being jealous. He then devises a plan to ambush Broly. But Broly, being extremely perceptive in his own way, senses Frieza's approach and is ready for the fight. As the fight progresses, Frieza realizes that Broly is much stronger than he expected and has to use all his dirty tricks to try and win. Or perhaps the plotline could involve Broly being captured by Frieza's forces, and then Broly breaks free and goes on a rampage against Frieza and his minions.
Power is a very common theme. Fans often explore who would be more powerful in different situations or how they could combine their powers. Another theme is rivalry, as they are both powerful villains in the Dragon Ball universe. Their personalities also play a big role, with themes of pride and ego often coming up.