New
#11
Yes, it is still linked to hardware. That has never changed. If you look at the device listing in your Microsoft Account you will see a list of DEVICES that have digital licenses for Windows 10.
Yes, you can still reuse retail product keys. The only obstacle is if it is a Windows 7 or 8 product key that has been blocked from online activation by Microsoft - then you would have to use other activation methods.
Licenses for Windows 10 are still issued on a per DEVICE basis, not a per user basis. Microsoft has only added the ability to store a DEVICE's license for Windows 10 in a user's Microsoft Account.