That sounds like a you thing; I've kept my macs for at least 5 years. My M1 is still going strong and I haven't felt any pressure to upgrade.
You will probably argue thats ok because you would have wanted one anyway by that time or some such point, but the fact remains that Apple will force you to upgrade your hardware not very long away by not allowing you to install anything on it.
Using your own conservative estimate, 8 years seems like a fine lifespan for a laptop, far longer than the "few years" you initially said. And in practice, there are plenty of macbooks that have been running even longer.
Thanks to the community, you can install macOS 15 (or older) on unsupported macs (as old as 18 years)
https://dortania.github.io/OpenCore-Legacy-Patcher/MODELS.ht...
This bullshit needs to die. The products are designed to last.
If you can load Linux on it it's still usable, but Apple OSs degrade rapidly after Apple stops supporting them. Apple is better about keeping devices on the latest OS version, but much worse about support after that period.
YMMV