How do you reliably (eg legally-definable) differentiate between "stopped supporting" and "haven't released an update in a while because it works fine and there are no major bugs"?
I accept there is some murky middle-ground so maybe there shouldn't be a start limit. You buy the hardware, you assume the right to alter what it runs (but lose official support thereafter).
That said - I think the above proposal is "release it immediately for the eventuality where they stop supporting it", not "require it be released when they stop supporting it".
So a very annoying bug that does not have any impact is major, or not major? Like my internet radio sometimes has connectivity issues. It resolves itself, but takes maybe 10-15s. After that, it works fine for a couple of hours of even a day. I wouldn't consider that major, because the product is usable in its intented way, it's just annoying.
Absent marketing to the contrary (prior to sale), I would consider a software defined radio that cuts out for 10-15s at a time defective. That out right breaks a lot of use cases. If that's a software (and not instead the result of something like damage to your particular unit) I would expect that to be fixed in a reasonable period of time for a product to be considered supported.