What would be the possible theme for "August 2026: there will come soft rains?"
In addition to--paraphrasing William Wordsworth--people's laying waste to their lives with the overuse of technology, Ray Bradbury's short story "There Will Come Soft Rains" has as it theme Nature vs. Science. For, as the very title suggests, despite the devastation caused by technology/science, Nature is a more puissant force. While humans have created such a thing as the atom bomb, capable of great destruction, yet scientifically able to counter this destruction with a house that resists destruction by a formidable bomb, fire, a natural force, is capable of destroying this house. And, in the end, even though the house is destroyed, the earth, albeit charred, remains. Thus, Bradbury's story points to the folly of machines that will overrule natures.
In my opinion, the theme of this story is that human beings are letting technology run away with their lives. The story is saying that we are putting too much faith in technology and that this will destroy us (perhaps physically, perhaps just emotionally or spiritually).
In this story, you know that there is "too much" technology because of all the things that the house is capable of doing. It takes over all these jobs that used to be human jobs until there is really no need for humans. In fact, we never see any humans in the story. So I think Bradbury is saying that we give up some of our humanity to the machines.
Bradbury then explicitly asserts the danger of doing this by having the house (and presumably the whole city and even country) destroyed by a nuclear war. Here we have technology literally destroying human life.