Presumably you're also paying a fixed monthly fee for "unlimited" broadband. It's likely you're paying per amount used for electricity and water. I'd bet your insurance is a fixed periodic fee with coverage capped at a certain amount. If my assumptions are correct, then your broadband services is already treated very much like your insurance service.
Most companies have overage charges you can elect to pay, instead of canceling your account. That would have been a good start.
Others mentioned not pretending to be unlimited. Actually charge for usage, instead. (I actually hope companies don't do this, as I'm WAY above the norm for usage.)
Another thing that some companies do is limit your speed once you hit the cap. That makes sure that you can do anything you -need- to, but can't go too much further over the cap.
The two arguments I still see against pay-for-usage models:
1. ISPs will structure the rates so that everyone ends up paying more.
2. The early adopters and developers that push technology forward are often at the high end of bandwidth usage, and in exchange for bringing new technology to the masses, the masses should be okay with 0.1% of their bill paying for the early adopters' bandwidth.
The analogy only holds if there was only one insurance company you could buy from who only offered a very small range of policies (none of which fits your needs).
Comcast doesn't have a monopoly in Seattle. There are multiple providers from which he could procure service.
Regardless, I'm curious what models people advocate. After all, there appears to be only one electric provider in Seattle. If we were, as proposed, to follow that model, then Comcast could negotiate to be the single service provider and then charge per usage. Is that more desirable than what we have now, where there are multiple providers offering different services at different rates?
If we're to argue for something different, we should be aware of what we're arguing for.
How do you propose things change?