Microsoft has proposed a model where they provide Linux security updates for 10 years, licensed separately from a device vendor that may go out of business. Let's see if Azure Sphere routers make it to market in 2019 - and at what price point. Maybe they can bundle the hardware in a single subscription service, or partner directly with cable companies.

You don't need a warranty to get kernel security patches _in practice_ if you run a mainstream distro on x86_64 hardware (which is available passively-cooled with low power consumption).