SFF and Worldbuilding overlap, as addressed by this question's answer. One site is "can it be done" and the other is "how was it done".
While I recognize that there are differences between the two sites, I want to argue that combining them would do more help than harm.
- Larger database
- More skilled or knowledgeable users in one place, meaning more answers; while not all expertise required in both situations is the same, there is a clear overlap in users, and both sites share the principle of "explain this"
- Questions never deviate greatly from science fiction or fantasy ideas in either site
- Tags would categorize "existing" and "theoretical" and sort the two sites information successfully into one site with similar information throughout
- Some information would not merge well, such as historical questions and meta for worldbuilding; that is where tagging would come in handy.
Side note: if you downvote please leave constructive criticism in the comments to help improve this question. You don't have to agree but help would be awesome :)