Rhino 6 WIP with mac license

Serengeti (Rhino WIP)
1

Would it be possible to test the Rhino 6 WIP for windows with a Rhino for mac license at some point?

2

You will be able to test the Rhino 6 WIP for Mac at some point:

3

Since Mac and Windows Rhino are separate products, the short answer is no.
When Rhino V6 for Windows is eventually released, you’ll be able to try the the public eval just like you can with Rhino V5 for Windows currently.