Just think how pissed you'd be if you just dropped 6k on a new Mac Pro that will be obsoleted in 3 years. Not speaking from experience, no sir.
And it’s much more likely that Apple extends this period for x86 than shortens it, given they might not be able to support Windows on Apple Silicon. And because they might need more than 2 years to build Apple Silicon Macs with performance as high as the Kac Pro.
But just because Apple comes out with a computer based on a new processor doesn’t mean your current computer stops working or stops getting updates.
The Apple // line was still getting software updates in 1991 and the Mac was introduced in 1984. Heck Apple sold the //e compatibility card in 1992 for Macs.
Apple supported 68K Macs for five years after the PPC Macs were introduced. They also supported the PPC Macs for either 5 years (10.7 came out in 2011) or 8 years (10.6 wasn’t classified as unsupported until 2014).
The same KB article indicates that what they consider to be obsolete (not at all supported) is hardware that is about 8 years or older, with most of it being 9+ years since first introduced.
Except for the original iPad. That still stings a little. They released it in 2010 and dropped support in 2012. But it was basically unusable with iOS 5 in 2011.