Promising eight years of firmware is easy. Keeping the toolchain that can build it for eight years is the part nobody costs.
What it takes
A pinned compiler, an archived SDK, a machine that can still run both, and a build that is reproducible from a tag. All four have to survive staff changes, and that is a documentation problem rather than an engineering one.
The last release
At the end of the eight years the final firmware is published unlocked, with the signing turned off, so somebody else can carry on. A product whose support ends does not have to become landfill on the same day.
