As varied as my participation in MathOverflow has been, I seem to gravitate towards number-theoretic issues involving $\phi$ and $\sigma$. I am considering writing an overlay article. This would be like a survey paper with a narrow domain: the MathOverflow forum corpus. The article would start with an acknowledgment that most of the material comes from mathoverflow.net, end with a list of specific questions and references used, and would attempt to summarize and integrate most of the material found on MathOverflow involving the sum-of-divisors functions and Euler's totient functions in number theory.
An upside that I see is that it would keep me from hitting the same sets of articles again, which have a fair amount of redundancy by now; others might benefit by looking at the overlay article first, and then digging around in the forum database for details. It would be better organized than the results of a search involving tags, and if community edited and reviewed, could serve as a useful reference in its own right.
A downside that I see is that it would quickly get outdated, as new questions and progress on those questions were submitted to the forum. However,the article could be structured so that new questions that were submitted could be linked to the article somehow, so that people looking at the overlay could check the Recent Developments section and find the link to the new submission.
There might be other upsides and downsides to the proposal of an overlay-survey article so tightly tied to MathOverflow. What are these upsides and downsides?
There are ancillary questions, if this turns out to be a popular idea: who wants to write an overlay, what topics should be chosen, should it be included under the purview of MathOverflow LLC, should it be independent scholarsfollowing an agreed upon format, and so on. But that would be getting ahead of myself. This question asks for the upsides and downsides; the ancillary questions can be asked and answered later.
Gerhard "On To Something Really Big?" Paseman, 2016.01.18