From what I've read
1) (this part is common knowledge) the Win10 upgrade for Win7 & 8 users is free for one year,
2) (this part may be new to some) the upgrade will continue to work for the life of the device,
3) what usually identifies the device is the main hard drive in the machine and/or the CPU.
 
As far as clean reinstalls go, if I have to go buy the full version of Win10 to do that, it's only going to be (OEM) about $125 or less. Considering how much I've spent on software, it's a drop in the bucket.
 
Identifying computers (devices or machines, however you want to refer to them) is done in several ways. This article explains the current thinking:
 
http://www.nextofwindows....ify-a-windows-machine/

MS will always need to be able to activate the software more than once. With the current systems if you reinstall and activate too many times too quickly using the same activation code the automatic activation will fail. I have had this happen before when I reinstalled windows 8 to get a clean install after having installed the upgrade on the same computer. The only difference was the hard drive. 
 
I called them on the phone and they asked me how many computers I was running the software on. Duh one. I just told them the old drive failed and I needed to reinstall on a replacement drive. They activated me no problem.
 
I'm fairly certain they will be able to do the same with windows 10. They know that hardware breaks and parts have to be replaced from time to time.
 
Also with windows 8 the downloaded install asked if you wanted to create an iso so for an offline install. That may be an option for windows 10 as well.
 
I registered 2 of my computers for the upgrade but I will wait to run it till I am certain of the procedures and make an image backup of my system before beginning.

I have the Win 10 preview installed on my backup system (on a separate hard drive).  I have Sonar Platinum installed, along with my Roland Studio-Capture, Frontier Tranzport (had to install this in Win 7 compatibility mode, but had to do that in Win 8.1 also) and BCF2000.  All work the same as they do in Win 7 and Win 8.1. 
 
I'm keeping a Win 7 installation (I need that for another application) so even if Win10 were to fall flat (which I don't see, so far) I'll still have a fall back if needed.

@Fireberd Well Roland Studio-Capture users will be very pleased for your confirmation that it works (helpful), although who knows what the final build will be like...

This latest build 10130 is getting very close, even the Microsoft comments on the build suggest that.  They even have it named "Windows 10" on the dual boot OS selection menu. Previous versions were labled "Windows 10 Preview".   I doubt that the hardware support (e.g. my Studio-Capture) will change in the final version. 

CNet is reporting that the Home Version of Windows 10 may force updates on the machine (http://www.cnet.com/news/windows-10-home-edition-may-force-updates/). This to me is very worrisome. I can see a number of scenarios that can cause issues, and not just hosing your system. Imagine having to do a presentation for a group, and instead of being able to go in and perform the presentation, your computer is showing that constantly spinning circle and saying "Windows is installing the latest update. 22% complete. Do not turn off your computer."
 
Even though I went ahead and signed up for the download, I may not install it. Somethings I should have the right to control. Like what is installed on my computer - and when.

MandolinPicker
CNet is reporting that the Home Version of Windows 10 may force updates on the machine (http://www.cnet.com/news/windows-10-home-edition-may-force-updates/). This to me is very worrisome. I can see a number of scenarios that can cause issues, and not just hosing your system. Imagine having to do a presentation for a group, and instead of being able to go in and perform the presentation, your computer is showing that constantly spinning circle and saying "Windows is installing the latest update. 22% complete. Do not turn off your computer."
 

While I'm not a fan of this move myself, there's a reason for the distinction between "Home" and "Professional".

Looks like my audio PC won't be getting any updates for awhile. It's offline anyway and the only time I connect it to the internet is to download win updates or updates from Toontrack, Cakewalk, etc... In this case win updates will be turned off.

I'm not seeing the offer on my 8.0 laptop... Maybe because I have 20 updates waiting to be downloaded/installed?

I'd like to try it on that machine before committing my DAW which is a comfortable win7 installation... Not showing the offer there either though it's up to date but maybe because it's online so infrequently?

Update KB3035583 is what does it:
 
http://www.infoworld.com/...ompter-downloader.html