Far better is to not use Windows 10 and tell Microsoft why.
...and I am writing this on a machine running (a much customised version of) XP, which remains completely silent on the network and never produces any traffic unaccounted for.
Microsoft doesn't suddenly decide to end support for something: it has a well-established, pre-published software life-cycle where operating systems are supported for 10 years. http://windows.microsoft.com/en-GB/windows/lifecycle
There's always a chance that a date will be extended, but it wouldn't be a good plan to bet on it.
Otherwise, I feel deeply sorry for you. Nobody should have to use inferior systems like Windows XP in this day and age. Presumably some badly-programmed bit of corporate junkware prevented you from upgraded to Windows 7 in 2009 .. ;-)
It's not just software tying a machine to XP but the hardware. A particular card may not have a 7 compatible driver. A penny-pinching executive will look at the very long number that is the cost of upgrading and decide to stay on XP and just replace parts (hard drive, monitor, etc.) as they break. Which may not be the smartest thing in the long run.
I can see 7 lasting longer than XP as it's the last OS built primarily for traditional Win32 (Desktop) applications. 8 and 10 are transitioning to an OS for managed code and virtualization. If you have a legacy application you'll get the best experience on 7 (or XP, or Server 200X). All of the improvements to Windows are meant to make C# based programs work better. There isn't much to gain by upgrading an older codebase to the new OS.
Of course people whose primary business is creating software think nothing of upgrading. To everyone else, writing new software is an expense. If the software you have does everything you need it to do, you're not going to rewrite it unless there is something to gain.
Aye, there's the rub.
Based on enterprise-class calculations (staff time etc), the cost of keeping an old XP PC running is dramatically higher than replacing it. You can get a tiny desktop with 4GB and a 1TB drive for less than $300, and cut your electricity bill as well.
In accounting terms, you may also save money by reducing reboots and fast start-up times, esp with UEFI. Whether Gartner averages apply in a specific case is, of course, an entirely different matter.
And, of course, if you've got a hardware lock-in that's no help at all ;-)
I agree with your final paras. We can see where Microsoft is heading. Where the world will actually be in 2020-25 is another matter....
Have you seen how extremely short-sighted and quarterly report oriented some executives can be. You say "only" $300 but I regularly replace $30 hard drives (that I charge $80 for) and they thank me for it because I'm "saving" them $200.
Now I regret cannot revert back to 7, without formatting. :(
If you don't need Windows but want support options then OS X is a fantastic platform too.
Or if you are comfortable using an enterprise class OS but are ok with looking after yourself in terms of support then you have many excellent options with Linux such as Ubuntu and its spin-offs as well as Debian or Fedora both of which I have superb experiences with on modern desktops and laptops.