You know what I have found out in my lifetime? I can speculate, and surmise all I want, but eventually all will be revealed. All I must do is sit back, and be patient. I know I will get my Windows 10, and I know I will be happy!
On a non genuine copy of Win 10, you can't upgrade to Final, can you get updates on non genuine windows, could not on previous versions
I wish it were as easy as you think, but what you have forgotten is Microshaft gives nothing away for free
Yes your OK as long as you have genuine OS under Win 10 to start, then you can format and clean install Upgrade to Final (GA) too
Here is what I would be concerned about..MS says you need a MS account and internet connection for the insiders program and I wonder if you also will for the free upgrade, I am guessing you do and you might even need both to install windows 10 at any time and if you do then watch out for subscription based windows in the future, just like office is going now. That is where they will make their money, not now but in the future.
So if I upgrade, my 8.1 key is turned into a 10 key? Also once I have done that, Can I do a clean install to 10 and use that key and be fully activated (since it was used during the 8.1 to 10 upgrade)?
You may be concerned about MS account, and internet connection, but I am not. I am on an MS account now, and my internet connection allows me to post to this forum.