I spoke with a computer scientist a few weeks who told me that in computer science there is something called a "vision paper", which is a paper that does not contain concrete results, but rather outlines a more general vision of what one either wants to do, or how a field may develop etc. A *future vision* in any case is presented.     
Searching the internet "vision paper" for computer science actually did not return many results - lest so for mathematics.

But maybe there do exist such journals that offer a home for such articles in mathematics and it just happened that I didn't find that. If you know of any, please let me know. The journal doesn't exclusively have to publish vision papers (actually, I think that would be bad, since it would probably be soon filled with all kinds of fantasies regarding how some subfields of mathematics might develop), but should *also* allow such papers.

I am interested because I myself am about to write such an article, and I'm not sure where to best post it. On a blog? I'd like to make it citeable and everything that purely online may vanish at some point in time (e.g. the blog providing company may shut down). A paper in arXiv? Would be an opportunity, but perhaps lacks in credentials.