Why not just sell new serial numbers which users can purchase and reactivate on their windows XP installs to get more support?
Many people like windows XP because it does all of what they need/ want to do on the computer, and on top of that, it is extremely fast on modern hardware, generally responsiveness that requires an SSD on windows 7, can be had with just a standard HDD on windows XP, especially in terms of boot times.
it is a light OS that only needs to really load about 40MB worth of data into memory in order to fully boot. it was designed during a time when hard drives were only a tiny fraction of the speed of modern hard drives.
For many users, they are using older computers that are doing what they need at a speed that they are comfortable with. Upgrading a older system designed for windows XP to 7, leads to an extremely sluggish experience, so for those users, even a free copy of windows 7 or 8 will not make them upgrade as they will likely still be a $500+ upgrade for the, all to do the same thing they are doing now.
To get an XP user to truly want to upgrade, you need to give a reason other than the OS is old, as that argument is similar to telling someone to stop using the wheel because it is old.
People buy and use an OS based on the functions it offers and what it allows them to do. (would you buy windows 7 if it came with no built in applications (just the desktop and nothing else), and no option to install other software or customize it?
The goal is to get work done and if the older OS is doing that just fine for the user then there is no reason to put money into upgrading it, especially compared to what that money can instead be put into.
For example, If the living room window of your home works perfectly fine, but the company that made the window comes out with a new model where the only change is a shinier bezel around the window. Now would that user pick the new window over upgrading from a 720p tv, to a larger 1080p tv for the same money?
Money is not unlimited and people look for value in their purchase. Will upgrading from windows XP give the basic user the same type of upgrade feel as moving from a basic bar phone, to a smartphone?
(Many of the customers I get, have no idea what OS their computer is running all they care about is if they can use the applications that they like to use, and now a virus or something is preventing them from doing that. The OS is not a concert until they try to do something that it doesn't support or allow)