The Xirus Alpha phase will be carried out for Rhino 5 only but the Beta version will be available for both Rhino 5 and 6.
Unfortunately, the Rhino C++ SDK is not available for Mac and McNeel doesn’t seem to have plans to make such a release any time soon. So, for the moment, we cannot provide a plugin for macOS. Still, we are keeping an eye on the Rhino-common development; maybe we can offer Xirus cross-platform at some point. In the meantime, you can try to use VMWare with Rhino and Xirus on it; this solution works well on our machines.