While you are absolutely correct in defining the legal word of "structuring" being confined to "Currency", there is far more to financial transactions than just a CTR (FinCEN Form 104) filing when making more than $10,000 in a currency transaction. You lump the CTR and SAR together, and the filing of a SAR is far different than an STR which only involved currency and specie. Rather than debate the word structuring, perhaps everyone should just look at a SAR.
Please note item #35 "summary characterization of suspicious activity"
Not only is "structuring" as legally defined in there, but 20 other activities that can generate a SAR.

And within the instructions for generating a SAR is the following: (my bolding)
"Any transaction (which for purposes of this subsection means a deposit, withdrawal, transfer between accounts, exchange of currency, loan, extension of credit, purchase or sale of any stock, bond, certificate of deposit, or other monetary instrument or investment security, or any other payment, transfer, or delivery by, through, or to a financial institution, by whatever means effected) conducted or attempted by, at or through the financial institution and involving or aggregating $5,000 or more in funds or other assets, if the financial institution knows, suspects, or has reason to suspect... "


While I am not going to argue about the actual definition of "structuring", I will say that the Feds have more than enough regulations that cover not only currency but all cash equivalents that one should not presume that because you are doing MSing, that your transactions are safe from scrutiny.
We are just a tiny bit of the underground economy not worth the time of the tax authorities or federal regulators.
If MSing ever became a national craze, then that could change.

However, every once in a while we get a thread where someone is visited by the enforcement arm of the IRS, which means that someone has their eyes on this hobby