I'm not saying it's trivial (it's not hard, but has a large enough amount of small actions to execute), but it's definitely worth doubling (or more) the phone duration.
The FamousProducer™ of my phone supported it for 3 years. This is terrible. LineageOS allows me to use it now - over 3 years after the end of support. Screw FamousProducer™.
Given that the S10e's battery life is already waning, I'm not sure I want to do that. But yes! If there were a safe way to do so, I would gladly run LOS on the phone for ten years.
Why be so coy about this? Naming and shaming should serve as a warning to those who might buy one expecting long term support, or as a spur to action towards LineageOS for those who many have been or are about to be blindsided by the support window expiring.
Another brand that seems to be well supported (although not as extensively, timewise, as Samsung) is Google. LineageOS still supports the Pixel 1.
My real problem isn't the previous 3 year window but that it counts from the first day they sell it, not the last. I bought my current phone, a Pixel 3a, late in its cycle for cheaper, early in 2020. It's now basically at the end of its updates because the guarantee counts 3 years starting from the release date in mid-2019, not from when I bought it.
5 years is obviously preferable but I'd like them to have also shifted it to be based on when they stop selling them new.