I think you're misunderstanding what I'm saying. The problem here is that Mac and Linux cannot be used to install packages built with VIPM 2017. I'm not talking about earlier versions.
You mention that having the source and build spec would allow someone to use a package on Mac or Linux, but that doesn't help at all in the most common case where only the .vip file is made available. As far as I know, all the packages on LabVIEW Tools Network, JKI Package Network, etc do not have source files and build spec available for download. This means that future builds of released packages made with VIPM 2017 will not be available on Mac or Linux.