It should be supported for at least the life of the motherboard
The life of a desktop or notebook is determined by the life of the motherboard and the solid state electronics on it. The mechanical bits, such as fans, disc drives, connectors, and the power supply with short-lived capacitors are easily replaced.
The life of a motherboard is at least 15 years, so an operating system that is sold for 5 years should be supported with regard to security and safety defects for 20 years from first availability.
Biting the hand that feeds IT
