one aspect where we think omp is a bit inflexible is the allocation of rights. You offer 5 permission levels, but there is no way of further fine-tuning as far as I know (apart from the stage assignment).
For us, the rights of the series editors are quite restrictive which entails more work for the press manager than is necessary. One thing is the right to create reviewers or enroll existing users in the “Add Reviewer”-Form.
To allow series edtiors to create and enroll reviewers, I have added ROLE_ID_SUB_EDITOR to the classes PKPReviewerGridHandler and SearchByNameReviewerForm. But this is not the solution we would prefer, because 1. the underlying problem (no flexibility) remains and 2. we would prefer to keep the omp-code unchanged (we only want to add changes via plugins).
Maybe there would be an way to add the configuration of rights.