If you remember, Mike, at one time you could activate 8.1 using a general key which was known during the 8 to 8.1 upgrade process. Prior versions of Windows came with some type of License key. With Windows 10, you do not need a prior license as long as the install has originally been done as an upgrade and activated.... As long as you have that same system configurations, you will not need a license key to install cleanly.
My current Windows 10 install was in the Insider program and was originally updated from 8.1. But the last several months, only clean updates had been done. It activated with 10240 and even after leaving the Insider program, it still activated. Another system which was not in the Insider Program, but upgraded normally and activated, has the same key as the Insider system.
Someone buying an OEM or Retail version of Windows 10, will have a license key but I have not seen one.
I suppose this will all be worked out, given enough time.