According to the SAFe Agilist 6.0 domain of Lean Thinking, a value stream is triggered by a demand for some value, such as a new feature, a change request, or a defect fix1. A feature is a service that fulfills a stakeholder need2. Therefore, a feature request is a valid trigger for a value stream.
A spike request is a type of exploration enabler that addresses technical uncertainty or risk3. A user story request is a type of backlog item that represents an end user goal or function4. These are not triggers for a value stream, but rather work items that flow through a value stream.