Judging by the comments here, if anyone uses a service they expect a company to provide support for it indefinitely. And apparently that also applies to hardware.
They're still supporting this device for now, so no complaints yet.
But when I buy a piece of hardware I absolutely expect it to work for at least ten years. When did that become unreasonable?
The base scenario is that it works standalone and it'll keep working for many years. If you choose to involve a server, then you have a responsibility to keep the server up for an extended period. If it's a legacy product then the number of users will continually drop and the cost to keep a couple servers up will be minuscule.
It's reasonable to expect it to function until normal wear-and-tear breaks it. After that, it's reasonable to expect it could be repaired at some cost.
However, it depends on a Google service — it won't work without a working Internet connection. This idea is fairly new for consumers.