I expect there will be literally millions of people still using xp when its support is cut down and eventually they'll all become spamy virusy hellscapes and they will probably resent Microsoft for it. I assume MS knows this. If it would support XP through 2020 I bet it would still have plenty of users.
If by 'plenty of users', you mean the tiniest fraction of 1% of Windows users, because by 2020 the driver support will have dried right up, in the same way that Win3x or Win9x drivers aren't available now for modern boards. IDE support will probably be long gone as well, AHCI only or better, which leaves the possibility of running an older OS pretty much impossible.
I enjoyed my time running NT4 and doing IDE driver hacks where NT4 IDE drivers weren't available in order to get DMA performance, but at some point I wanted USB support, you know?
Though it would be interesting to see what take-up there would be if Microsoft was to say "Ok, we'll continue supporting XP for another ten years if we can drum up x amount of money in 'extended licence' fees, everyone who wants to use it for longer and still get security updates needs to pay <whatever the cost of that XP licence is in that country>. I can think of quite a few small businesses I know to which that would make a certain amount of sense as they're stuck running XP due to legacy hardware/software support*.
Note that I say "interesting", not "good"*, because there comes a time when people must move on. Also, the likelihood of even the best quality kit lasting another 8-10 years stretches the bounds of plausibility IMO. A lot of boards don't make it to 8 years, let alone 20.
* - because the purveyors of said "legacy hardware/software" will be even less inclined to full their finger out and start developing for newer platforms, which they should have been the moment Vista went into beta let alone now.
I've already countered your point about people resenting MS for not supporting their products forever:
http://forums.anandtech.com/showpost.php?p=34160651&postcount=64