How long is long enough to avoid breaking something the users depend on? One more year? Five years? Fifty? I think we can all agree that it's reasonable to drop support at some point, making it just a question of when and at what cost.
10 years - a piece of software compiled with 'supported' libraries, SDKs and what have you should function for 10 years. An appliance or a service should function for 10 years and have spare parts avaliable for that long.
That is the guideline I ise as a consumer, if I can see that something won't last a decade, I won't be spending money or time on it if i can avoid it. At that point it's no longer a durable good, it's a consumable.
They could drop it with v12, or wait for v13, both would be fine. Dropping it in the middle of release cycle what people are objecting to.