The standardized format part appears to be a solved problem.
It isn't solved I assure you. EDI is useful but not easy or simple enough to be universally implemented. EDI generally only gets used by rather large organizations and it doesn't fit so well with the sort of spot buys that smaller companies tend to engage in. It tends to require a lot of process change rather than being an adaptation of existing processes. Setup is generally too hard and expensive. Think of it a little like using FTP vs email for file transfer. FTP better designed for the actual transfer of files but it's harder to set up, has more transaction handshake overhead for the user, not as useful for one time transfers, requires more training, and users already have email and know how to use it. Despite the fact that using email is technologically worse in a lot of ways it fits people's workflows a lot better so it gets used. Current EDI implementations suffer from basically the same problem.
Given my allergy to "screw the customer as hard as possible" business models,
That's why some sort of open software here would be a huge blessing. Few companies really want to be tied to some proprietary software if it isn't necessary. I would be delighted to see some EDI equivalent to Apache - an open source solution that works well for most and is relatively easy to put in place. Hell it could be as simple as emailing and receiving documents from some piece of middleware which requires relatively minimal changes by users.
I'd sooner write a system that takes advantage of communication systems businesses already have, rather than try to collect extra.
Nothing wrong with that if it gets the job done. I certainly would prefer something that is based on something already well understood and preferably more open. No sense reinventing more wheels than necessary. In fact you would have to at some point implement some way to talk with existing EDI systems because a lot of them are already implemented and they aren't going to get torn out.
To be honest, if Intuit had a brain in their skulls they would implement some form of EDI directly into their software that made document exchange easier and reduced paper shuffling. But they don't seem to be interested. Hell their ODBC drivers were developed by a third party, even the ones they include with their more expensive packages. You would think that would be something they would want to control and use but they don't. Their internal databases appear to be some sort of non-standard home rolled junk.