Will Windows Support be Extended?

Not likely. XP got a reprieve because Vista took several years longer than expected to finish, and even then it was a pale shadow of what was promised during that time, giving XP more than the usual 3 years (at that time) to become entrenched in both home and enterprise environments. This is basically why NT4 got a reprieve before that, because Windows 2000 took a bit longer than expected to come out, but then neatly laid out the groundwork for XP which came along about 1.5 years later.

Part of why Vista took so long to develop is that Microsoft was forced to rewrite big chunks of the internals. These aren't the "sexy" sort of changes in the forms of features that users will see and interact with, but they are absolutely vital nonetheless. One example is how Microsoft rewrote the process scheduler in Vista to work more efficiently with multi-core CPUs. Before it was geared towards multi-CPU systems and there's a subtle, but significant, difference between those two that can have a large impact on overall performance and responsiveness of the system. Microsoft also basically chucked out the entire graphical interface and rewrote it from scratch using the DirectX API. Where before it was a software rendered 2D pile of crap that should have been put out of its misery ages ago known as GDI+, now there's hardware acceleration on the part of the video card and it opened the door to all kinds of things that you couldn't have done with GDI+ like have live previews of a window if you hover your mouse over the task bar entry for it.

Despite how badly it was panned by users, you didn't see a lot of developers complaining about Vista, because they were aware of all the under the hood changes made which would lay the foundations for what became Windows 7. If you take away the incredibly stupid move of ramming the Metro UI down everyone's throats with Windows 8, it too is a solid OS that was only made possible because of the work that went into Vista. This is what will make it possible for MS to put out new releases in it's typical 1.5-3 year cycle depending on if it's a minor or major update. So don't expect to see Windows 7 getting any kind of reprieve like XP, since by 2015 we'll probably be seeing Windows 9 come out, and by 2020 who knows. But basically rumor has it that Metro will either be going away completely or at least not forced upon you with Windows 9.

For the average user the change from main>ext will mean zip.

http://www.pcworld.com/article/2010820/how-long-will-microsoft-support-windows-7.html

I'll start to worry about it in 2020.