Well the process will not be voluntary, it IS mandatory as of the date the signed executive order goes into effect. The wording of these snippets is not the wording of the actual executive order. I have read Executive Orders pertaining to safeguarding classified information and they are not vague, they are specific and fully encompass the topic of the order.
Someone give us a site that has the language that says it is mandatory. I don't see that in the texts on line. The issue whether there is a mandatory private sale NICS as compared to setting up something private citizens must use.
If that is true - it isn't in the White House PDF.