Edit: this question is not a duplicate of the one that has been mentioned in the comments, as I am here suggesting a built-in feature to allow HSM as a potential site to migrate to within the reasons-for-closing section.
Recently, one of my questions was voted for closing with a reason that could apply to any question with the math-history tag: should be migrated to History of Science and Mathematics.
Since I'm not particularly against this migration (I simply had never heard of HSM upon asking the question), I tried to close the question myself, yet I couldn't because as of right now, you can choose the site to migrate to only from a list of three, and HSM is not one of them (see below). I think it should, even though HSM is still beta, as it will save time and as there is every reason to believe that HSM will flourish and become a full site.