This is not likely to be implemented, nor is it a desirable feature. First, recall that even posts on another SE site (e.g., MathOverflow) cannot be used as duplicate targets, even though they have the same Q&A format. If cross-site duplicates were implemented, they would be implemented between different Q&A sites first; but that is not happening.
Second, I think this is not a desirable feature. One of fundamental principles of SE is that everyone can answer a given (non-closed) question, and the best answers rise to the top; additionally, the question author is able to select one answer as most helpful. None of this is available on a blog. Robin's explanation of differential forms on manifolds may be great, but a calculus student confused by $\Delta x$ and $dx$ in "thin slice" integration problems might find it hard to follow, especially since they likely had no multivariable calculus yet. On a Q&A site, there could be other, more accessible answers. Not on a blog.