Currently, using generated PKs explicitly prevents multiple inserts from using a batch-bind insert. This is unhelpful since switching to generated PKs could potentially cause a performance decrease for certain use cases because of the lack of batch insert functionality.
This is prohibited by the existing BatchAction:
Having done very brief performance testing against PostgreSQL, the performance difference turns out to be minimal for a realistic production scenario, but even so, this is a restriction worth removing I think.
I have a pull request coming for this.