I have seen many times that client wanted to migrate or do a large change in the infrastructure. A change could be to move away from Business connector to SAP PI or introduce a new data model between the EDI XML and IDOC XML parts. Today I was talking with a potential client about how to perform test, when they wanted to swith from mapping from the INVOIC02 idoc to map from a custom datamodel based on the IDOC. This does give them some more flexibility, but also require a lot of other work.
Most integrations solution working with SAP PI and EDI is a complex or even very complex. So there are a lot of things that you will not often catch.
To be sure that you can do something like this requires a lot of testing. This presentation gives some ideas on you can test your solutions better.
If you want you can see the tool that I have created PIMigration take a look at PIMigration.com. PIMigration is a product that I have developed to help make it easier to perform this kind of testing.