In recent years, the simultaneous delivery of mixed ion beams has been explored as a method for treatment monitoring in ion beam therapy. A promising proposal involves a 12C6+ beam for treatment with a small 4He2+ contribution for imaging, taking advantage of the fact that 4He2+ has a range in matter approximately three times greater than that of 12C6+. Slow extraction of such mixed ion beams with similar, but not identical, charge-to-mass ratios (e.g., a 0.065% difference between 4He2+ and 12C6+), comes with its own challenges. Depending on whether the mixed beam is generated in a single ion source or by sequential injection from two ion sources into the synchrotron, the horizontal phase space distributions of helium and carbon can differ noticeably. Along with an energy-dependent offset in magnetic rigidity, this can affect the helium-to-carbon ratio delivered throughout the spill. This contribution reviews ongoing developments in mixed beam slow extraction. Recent measurements at GSI and MedAustron demonstrate how adjustments to chromaticity and RF kock-out excitation parameters can be used to tailor the extracted He:C flux. The measurements are supported by Xsuite simulations, which allow tracking of particles with non-reference charge-to-mass ratio. Additional options for creating mixed beams of ions with significantly different charge-to-mass ratios open up if the synchrotron supports employing two independent RF frequencies. A first step has recently been taken at GSI by demonstrating simultaneous acceleration of iron and bismuth. Finally, some examples for the application of mixed ion beams beyond ion beam therapy are given.