As for sticking strictly to presently known science, I will simply point out that we have already experienced at least two major revolutions in science in this century alone.

It's most presumptuous to believe we already know all the answers and will never get any more big surprises.

Of course, the way writers think about those things is almost certain to be affected by their own cultural background, and it would be hard to deny that, for whatever reasons, a lot of SF writers come from Anglo or European backgrounds.

I think the rising and falling popularity of areas like hard SF and far-future SF is, to a considerable extent, the same as any other fashion.

I think the international appeal of SF is quite understandable since the kinds of people who like to read it, are, by the nature of the beast, interested in other cultures, of which other nations on Earth are the closest available example.

As for sticking strictly to presently known science, I will simply point out that we have already experienced at least two major revolutions in science in this century alone.

Resist the temptation to try to use dazzling style to conceal weakness of substance.