The excellent Splatoon Raiders is fairly content-packed though some were hoping that it would replicate the mainline Splatoon games and get a hefty expansion. Sadly that is not the case as in a recent interview with Famitsu the development team have stated that the game was created to be a “complete experience” and therefore they have no plans to add additional content via DLC. Here’s what was said via machine translation.
Do you have any questions about DLC or updates, which have been a frequent topic of discussion among readers?
Inoue: Unlike the main series, which evolves the gameplay through balance adjustments and content additions, Splatoon Raiders is developed with the goal of providing a complete experience as is.
Therefore, we are not planning any DLC or updates that affect game balance. However, if a critical bug is found, we will address it as needed.

That’s a shame. Oh well.