Lesen der EULA hilft:
https://www.microsoft.com/en-us/Useterms/Retail/Windows/10/UseTerms_Retail_Windows_10_English.htm
4.b: If you acquired the software as stand-alone software (and also if you upgraded from software you acquired as stand-alone software), you may transfer the software to another device that belongs to you. You may also transfer the software to a device owned by someone else if (i) you are the first licensed user of the software and (ii) the new user agrees to the terms of this agreement. You may use the backup copy we allow you to make or the media that the software came on to transfer the software. Every time you transfer the software to a new device, you must remove the software from the prior device. You may not transfer the software to share licenses between devices.
Man beachte den die Ergänzung mit dem Upgrade. Also Retail 7/8 wird zu Retail 10. Wie sie das technisch machen ist sicher noch unklar, aber rein rechtlich sehe ich zumindest für die Retailer kein Problem, und ich würde sie auch darauf verklagen (ich habe von retail aktualisiert). OEM User sind allerdings angeschmiert, das ist schon so.