thanks to Szymon from support for taking the time.
Maybe I have a problem to understand the license model.
1. does it mean every 72hours the current key file becomes invalid and is going to be replaced with a new one ?
Yes. After 72 hours (in case you haven't used the acquired License Key), you are required to download another license key.
2. if I frequently change the entire OS and back it up in an OS image, I am requested to download a new key file on each new install, is this correct ?
The assumption is - no, you are not. The once activated plugin should maintain in this condition.
3. that means we have unlimited access to the ever replaced key files and are downloadable when needed ?
Yes.
4. what happens if a key file is not available (i.e. server timeout, technical issues, company discontinue etc.) ?
We are avilable here daily. Will get you out of trouble!
5. will this license model be applied to all new upcoming releases, which means no more permanent and restoreable licenses ?
Yes. But, mind, the License Key you activated your plugin once for the first time, can be left within your hard-dives,
as it will serve your Activation ever since the first application. This is just a safety procedure.
I am still puzzeled and not getting warm with the license model,
but will give it a try to evaluate issues in a practical context.
The screenshot on the first page is Devastor V1. Here's the new V2 GUI screenshot. Beautiful. I hope all other fake 3D perspective supporters will change their minds, too. There are not many left anyway... Klanghelm... Sonimus... 
and just a couple of others. I'm so rejoicing seeing vectorised resizeable GUIs with no fake 3D perspective coming. Great! 
