The Others in Pluribus are so tranquil and peace-loving that they somehow come across as strangely sinister, which makes me think they aren't quite the wholesome beings they seem to be. Instead, I think it's more likely that the takeover of Earth is part of a much grander plan, and one that doesn't paint them in a very good light. So far, it's been tricky to objectively label the Others as villains, but that could easily change if a certain narrative avenue is explored.
The key to my theory is the group of 13 individuals who, for reasons that have yet to be explained, weren't brought into the Joining when the rest of the planet's population became one big hive mind. Rhea Seehorn's Carol Sturka is the most prominent example of this type of character, but the other 12 are equally relevant to what I'm about to suggest might happen as Pluribus continues.
The Joining would probably get bored if they successfully brought the unjoined characters into the hive mind
The individuals who have been introduced in Pluribus so far all have different views about the Joining. Generally speaking, Carol has been in the minority with her view that the Joining is a bad thing and should be reversed, but the same is also true of Manousos (Carlos-Manuel Vesga). However, although figures like Mr. Diabaté (Samba Schutte), who have embraced the Joining as a concept in the abstract, prefer to reap the rewards while remaining as an individual.
Interestingly, Pluribus episode 7, "The Gap," ends with Carol in an emotional place that makes her more likely than ever to become one with the Joining, which can only happen with her consent. Similarly, Manousos being rescued by the Others in the same episode may contribute to changing his mind. Pluribus seems to be gradually giving the individuals good reasons to become Others, and if they all agree to be part of the Joining, a very compelling question is raised.
What does the Joining do when there is no one left to interact with? The Others are all joined via a "psychic glue" that maintains a constant connection between everyone in the Joining. In other words, they all know what the others are thinking, because they're always thinking the same thing, and can even access each other's memories. One shared consciousness across the entire planet is basically the same as there being just one person remaining. So, it's logical to assume that the Joining would get lonely if and when that time should come.
The Joining getting lonely after assimilating a world would explain the mysterious RNA transmission
Pluribus' very first scene revealed how showrunner Vince Gilligan planned to make his hive mind premise possible. A signal picked up from somewhere in deep space ultimately turned out to be instructions for a specific nucleotide sequence. When Earth's finest minds finally decode it, the instructions are followed. The virus then spreads around the world and connects the infected minds together. The show still hasn't revealed where the transmission came from, or who sent it, but I think I might have figured it out.
Assuming for a second that the Joining will succeed in convincing every individual to become part of the hive mind, then the very nature of the Joining suggests they'll start looking for new individuals and do the same again. With no one left on Earth who fits that bill, the only other option becomes other planets. Therefore, the Joining could then transmit that same "recipe" for the psychic glue into space so that another world can receive it, even if no one picks it up for centuries.
If this is true, it comes with massive implications for Pluribus canon. Firstly, it would essentially confirm that Earth isn't the first planet that has been impacted by this transformation. In fact, it makes it impossible to know how many planets have experienced the same thing. Secondly, it makes it possible that the Joining's goal is to spread throughout the galaxy, and possibly even the universe.
Finally, if the Joining itself is boosted by the signal that's received and transmitted between planets, that means the Others aren't just human, but also have alien memories and thoughts in their minds as well. A one-off occurrence of enforced planetwide peace is easier to describe as wholesome. A compulsive need to keep spreading as far as possible feels far more like a hostile takeover. When there are no more worlds to "conquer," what then?
An interplanetary Joining would (sort of) give Pluribus an additional genre label
Although Pluribus is certainly an unconventional show for any genre, there's no doubt it's solidly sci-fi. That said, there are several subcategories that can separate sci-fi stories into more specific piles. For example, while Pluribus' version of the end of the world is very different from The Last of Us' apocalyptic setting, they share the post-apocalyptic subgenre label. If the Joining originated on another world and plans to spread even further after Earth is fully infected, then Pluribus is technically a space opera.
Space operas generally show what's going on among the stars, with scenes filled with starship battles and alien summits trying to come to territorial agreements. Those tropes would not mesh with what we know of Pluribus so far, but that doesn't necessarily mean it's not all happening offscreen. In fact, the very fact that someone transmitted the RNA instructions from somewhere in deep space has already confirmed the existence of sentient extraterrestrial life. This lends even more credence to my Pluribus theory, making it more likely to be correct.
Pluribus season 1 is streaming now on Apple TV.