Comcast Has Tested Pay-Per-GB System - But is afraid to implement it for fear of pissing you off?

We noted yesterday that claims that Comcast's invisible cap is 90GB were incorrect. Today, you've got the Consumerist insisting said cap is 200GB -- which also isn't necessarily correct. While 90GB or 200GB caps may exist in some markets, they aren't the system-wide limit since, technically, the caps change based on congestion and vary from market to market (sometimes as high as 500-600GB). More interesting in the article is an insider's claim that Comcast has a "pay-by-the-GB" overage system already tested and ready to roll:

"Comcast even has a system ready to go where if you exceed the limit a popup will ask you to purchase additional gigabytes, our source says. The graphic interface is completely designed but they haven't deployed it because they're waiting for either another ISP to do it first or to figure out how to do it without angering their customers. CEO Brian Roberts is said to have seen a demo and given his thumbs up."

As we mentioned last week, there's plenty of people in the industry who'd love to shift to a bill-by-the-byte model as a way to address "bandwidth hogs." But which provider wants to be the first to implement such a system and face the marketing wrath of its "unlimited" competitors?