The performance of two microgravity measurements of the Soret effect in molten salt mixtures has led us to analyse their insufficiencies, essentially in terms of hydrodynamic diagnostics. As a consequence, and after preliminary measurements on Earth of the Soret effect on a particular class of vitrifying liquids by means of a holographic technique, we propose, in collaboration with two other groups, a new microgravity experiment on molten salt mixtures. The scientific interest and feasibility of this new experiment are analysed in detail. New solutions are given to overcome the experimental problems of such an experiment which should provide decisive proof of non-convective experimental conditions in space for molten salts.