Yes but what is the right price for a one-time payment of software ? If you're going to use maintenance, updates, all the work that comes after you paid, what do you consider is a correct price to pay in advance for all future changes ?

The "correct price" depends entirely on the specific software, so this is an impossible question to answer in its literal sense.

> what do you consider is a correct price to pay in advance for all future changes ?

You don't. Outside of security updates, which should never be charged for, you pay for the software as it exists when you buy it. When future changes come around, you buy the upgrade (if you want it).

It's the tried-and-true method of charging for this stuff.

We're specifically talking about an OS here, so the scope is not really the same, but still: are you ok with no package updates ? No update to the documentation, the wiki, and stuff like that ? No forum or chat ?

>Outside of security updates, which should never be charged for

Why shouldn't you be charged for for security updates?