Not convinced this will happen. Plenty of k-12 Chromebooks with an extended support life to 2032+. Having used both seems to be still quite a big task to merge these together.
This could be the "next generation" ChromeOS that are exclusively available on new/recent Chromebook devices, while Google keep updating the "legacy" ones with only security patches. From what I can tell, Google never explicitly promised that every supported Chromebook can get the latest feature updates. The only said "updates".
Of course this is pure speculation and I'd love to be proven wrong.
