It's most presumptuous to believe we already know all the answers and will never get any more big surprises.
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.
It's easy to imagine ways the future can be ugly and depressing. It's harder, but more worthwhile, to imagine plausible ways we can make it better.
Its limitations are those of the physical universe: it won't let you play with some really wild ideas that aren't possible, but are fun to speculate about.
What SF can do better than anything else is show us the range of our possible futures, and what we can do to realize the good ones and avoid the nasty ones.
This means I must pay close attention to the writing, but equally so to the scientific background - which sometimes means doing fairly involved calculations.
There may be something to the suggestion about the pace of technological change intimidating writers, though - it's been awfully hard to keep ahead of real developments.
Ideally, I'd like every issue to include a diverse group of stories that meet the qualifications sketched above, but covering a wide range of specific matter and flavour.
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.
And, of course, some SF is set close enough to here and now that Anglo and European do apply. Since many of the writers come from those backgrounds, so does much of the fiction.