The life-span of Windows 7 is not heralded or predicted.. yet. It should be viable for at least another 7 years, hopefully! Here is the 'inside info" direct from M$ concerning EOL for Windows XP~Win 7
Windows 7 was created to "exorcize" the errors of Win Vista. But in that motion, Win XP was given an extended life term. While Win 7 fits most general use categories for computers and laptops, the Win 8 version will be more centered around hand-held pads and tablets.. superior to the "CE" version and has resident features for 'cloud' computing needs, plus the touch-screen and virtual reaction interface. Not to mention the "on-the-fly" EFT transfers! Yet Win 8 will still be compatible to older use intents.
As to older Windows OS versions, Win 98 was the "last of the breed" to have a true command-prompt mode.. and is vital where older programs are not compatible with 32-bit OS platforms. While W2K and newer versions have the 'command' mode, it is not as versatile as true 16-bit command mode.
F@H.. to solve mankind's maladies.. in our lifetimes!