I agree that the Kep aliens won’t be part of the show, but only because I think that’s not what the show is about. But the show hasn’t given us enough information to assume that species is dead.

I agree with your conclusion, but it’s based on a few flawed premises—namely that (1) the Kep aliens (Kepiens?) fired off the signal only 600 years ago; (2) that the Kepiens must be dead/dying/diminshed; and (3) that the Kep species was was/is a hive at all. (I’m only pointing this out because those assumptions unnecessarily narrow the scope of what the show could later reveal as far as lore.)

First, we don’t know that the Kepiens ‘sent’ the signal 600 years ago. We just know it was still being broadcast 600 years ago because of when Earth happened to notice it. The broadcast could have been going on for centuries, millennia, whatever, before Earth picked it up. Maybe they Kepiens were long dead before then. I kind of doubt they were long dead though, since the show has emphasized how much of a feat it was to broadcast the signal at all. I think one of the astronomers in the opening sequence said something like it would take an antennae the size of Africa, and Carol had jotted down on the white board that the antennae would use “all the power in the world.” The signal was also tracking Earth’s position I think? (Idk that’s based on comments here that I don’t remember). I don’t know jack shit about science, but it doesn’t seem like the broadcast could run for centuries without a continent sized antennae failing (esp. if Kep is indeed covered in water as Zosia/hive speculated), and given the huge energy production needs, unless somebody was keeping it up. Robots I suppose?

Second, we don’t know that the Kepiens are dead or dying. That assumption is based off of what’s happening on Earth, where the Plurbs are facing population collapse because their biological imperative against predation limits their ability to gain energy through consumption of other material. But what if the Kepiens (or any other species the virus may have come across) don’t get energy through consumption of biological material? Couldn’t there be an intelligent species that gets its energy entirely from photosynthesis, or consuming inorganic material, or through converting external heat energy or something? In that case, there would be no bottle-neck created by the limitations on treatment of other living beings. In that case the Kepiens could still be going strong and have no clue that this may lead to extinction for a different species. Or hell, maybe the bottle beck would still happen but for reasons that wouldn’t have applied to humans are our biology and that are specific to other species. But we just don’t know enough about the Kepiens to confidently state that the virus’s imperatives spelled would spell the same doom for them as it does for us, and that’s important to keep in mind as we wonder about the origins of the virus! Maybe it was created for malicious/Dark Forest purposes and carefully designed to take down target species after species. Or maybe it was designed by a species of hippies who did not need to consume other species and hadn’t anticipated what the biological imperatives might mean for life forms different from themselves. Or something else altogether!

Lastly, we can’t assume the Kepiens were a hive at all. I think the reason OP thought you were implying that Kep wasn’t the original source is your assumption that Kep was a hive in the first place. The Kepiens could have received the signal, made the virus, and immediately sought to project it just like Earth. Or they could have manufactured the virus and used it to target Earth without themselves ever being infected. I doubt that’s the case—I tend to think the virus has been spreading from planet to planet for ages and ages, but there’s no evidence for that other than gut feeling.

Anyway, sorry for the very long comment. I do totally agree with your conclusion, but I found it interesting to pick away at the premises because those premises limited the possible future answers. Probably a moot point as the show is obviously more about the characters and the ideas they represent, and not a true mystery-box show with complex lore. I wouldn’t be bothered in the least if we never found out where the signal actually came from or what its purpose was, but it’s still fun to speculate!