As spotted by Tech4Gamers, Shift Up has posted a job listing for a combat designer — but more specifically, it alludes to the creation of new enemy types. Given that the listing exists in relative isolation, it seems more likely that this is related to DLC, rather than a full-on sequel. Still, it's an exciting prospect all the same.
Obviously, we don't know how significant this supposed DLC will end up being, but Stellar Blade's existing, mostly linear structure lends itself to additional adventures. That said, the game only launched a few months ago — and so it could be a while until we get any official word on what's next.