> In the end "help with migration to" isn't the same supporting the existing product.

I don't know that that's clearly true. Apple gives at least 5 to 7 years of updates past the last sale date for computers. (I don't know if this is an explicit promise or not; they have an explicit hardware support for 5 years and limited support for vintage [5-7 years old] equipment.)

I don't think I get to demand 5 years of support for specifically Sonoma or Tahoe on that equipment, but rather just N years of "some usable version of an OS and support to transition to it".

Replacing ChromeOS with GooglebookOS 8 years from now seems not that different from replacing Tahoe with Golden Gate.

The other alternative could be "we still support ChromeOS for 10 years, and will release security patches for all critical vulnerabilities that we find and fix after 2034" (but we might privately not look that hard for them...)