Is a System Landscape Directory (SLD) still required in the landscape?
Yes. The interaction between the System Landscape Directory (SLD) and the Enterprise Services Repository is just the same as in the case of ES Repository. You can define the products and the software components in the SLD and import them into the Enterprise Services Repository. With the Enterprise Services Repository you have the additional functionality to create local software component versions which are local to the specific ES Repository and are not visible to the rest of the landscape (and which can therefore not be transported from one ES Repository to another).