One of the key deliverables a Business Analyst produces is a list of features that any solution must include in order to meet user requirements. This applies to vendor implementation projects as well as custom development. Developers need to know what featuers to develop, and a vendor product selection effort needs to know what features the product must contain.
This all ties in closely with scope. As features are identified, governance stakeholders will make determinations as to which features are in scope and which are out of scope. Scope management is the purview of the Project Manager, but the identification and management of the scope items to be taken into consideration is the responsibility of the Business Analyst.