There is nothing in the FAQ or here on meta that says these questions cannot be asked, but they usually either
- are answered with a quick look at Wikipedia or
- encourage pointless speculation
Shall we close these as off-topic?
Because they will encourage speculation, and not hard-and-fast answers, I say yes, those are off-topic. The motivation for StackExchange sites is the answering of objective questions, in a timely manner. Since we can not be objective and timely at the same time when answering these, we should close them.
Duplicates should be doubly so closed, as the system will eventually delete those.