We're currently working on an event registration package which needs on-line billing. I've been working on a general_billing package which could eventually be inserted under the e-commerce package, but it would be much more lightweight for purposes that don't require all that stuff. However, all this talk of Verisign and stuff leaves me wanting a little more information on your payment gateway service contracts. We are on a short timeline for our prototype, but perhaps by the time our project is concluded, we can bring these two things together.
As for the initial question on this thread, I should be able to release the general_billing data model and API fairly soon. Looking through the ecommerce data model, I see a pretty easy pathway to making it an "extension" of general_billing. And billable content, or event registrations, or room reservations, or whatever, can be done without wading through the whole ecommerce juggernaut.
