BPMN21 — UML interface operations do not match BPMN interface operations

Currently interface operations in BPMN follow a "Document" model where all the arguments are wrapped in a single "Message" in and out of the operation.
But in UML, interface operations follow the "RPC" model, where arguments are independent and each one has the "In, Out, InOut" classifier.
This difference creates several problems when trying to relate/map BPMN and UML operations. Another side effect of the BPMN message model is that you cannot use simple data associations to fill the arguments of a service call. Since the operation is a single type, we have to use transformations to target the arguments (in my case we hide this complexity from the end user, and probably every vendor will do the same.

So, if the FTF wants to have a reasonable integration with SoaML, we should fix this issue. The proposal is to adopt the UML model, with separate arguments instead of a single document in and out.
We understand this is a major change, and a migration path from the Beta spec to the final one is a mandatory requirement.