From the article, "Even a certified device could have a commitment to support for only five years after the release date of the underlying version of Ubuntu Core. That means you could have a certified appliance based on Ubuntu Core 18 and it might only be kept updated until 2023 (though the OS itself has updates at least until 2028)."
And here is the major problem (and not just with this Canonical project). Support should be for x years after EoL, not from release. I'm also a strong advocate of legislation making EoL software open source, to reduce the deliberate obsolescence manufacturers insist on.