For this talk my starting point will be the conjecture of Charles Doering and Christopher Miles (stated in “Diffusion-limited mixing by incompressible flows”, Nonlinearity 2018) regarding “convergence to the Batchelor scale” of a suitable norm for mixing in passive scalars. I will sketch and contextualize my recent result in collaboration with Steffen Pottel connected to this conjecture and finally describe open problems and possible intermediate steps to the conjecture.