In arXiv: 1404.1003, we develop a fully flavour-covariant formalism for transport phenomena. A significant and novel element of this formulation is the inclusion of rates that carry higher-rank tensorial structure in flavour space. In this talk, we illustrate the necessary appearance of such rates by means of a generalization of the optical theorem, making connection with the unitarity cuts of partial non-equilibrium self-energies. In addition, we describe the flavour-covariant canonical quantization of spinor fields in the presence of spatially-inhomogeneous and time-dependent statistical backgrounds. Finally, we highlight the need for thermally-corrected real intermediate state (RIS) subtraction and comment on potential implications of our approach for quasi-particle approximations in the field-theoretic transport equations of the Schwinger-Keldysh Kadanoff-Baym formalism.