This question: What is a "Space elevator"? was migrated to the space exploration SE. Whats the line between astronomy and the Space exploration SE site? The name would suggest that all space exploration questions are on topic on this site, but not vice versa. Is space exploration for technology around space travel? What kind of questions are better fit there than here on astronomy?
You can see on the on topic section of the help page for our site what is in scope here. A space elevator is a device (large-scale equipment) which does not directly support astronomical observation or data gathering, so questions about it are off topic. Now, a question about how a space elevator might be used for astronomical data gathering would be on topic, though probably too speculative at this point. A question about how we might observe space elevators around other worlds would also be on topic, though that might also be too speculative.