Leaving the new question open defeats the entire purpose of SE. If I find the newer one it might have a link to the older one, but if I find the older one, hardly ever has someone gone back to update it with information from the new one. This is exactly the kind of problem that happens on forums, which SE was designed to solve, and why questions can be closed as duplicates at all.
You could, I suppose, delete the entire old question after the new one has been approved. That solves that problem, but raises a host of others. A better approach might be closing the old question as a duplicate of the new one, but that's definitely going to be confusing sometimes.
Making the question CW seems irrelevant. Why would you do that? You can edit (or propose edits for) any question/answer. CW is more about questions where rep generation or "the single right answer" makes little sense.
I still don't see a concrete problem here. "The field advances", yes, but not very fast, and rarely in a way that invalidates truly good answers. (Admittedly, I view that somewhat tautologically - one characteristic of a truly good answer is that it rises above the immediacy of "this exact thing is what you do right now with this API-of-the-week/month/year".)