For such a high temperature, and considering the corrosion and reactivity of salts, it might be useful to consider fluidized solid particles as a means of heat transport in lieu of the salt. It is routinely used today for such a purpose in CFB circulating fluidized beds at about 700 C, and the heat transfer to the superheater in the cyclone solid's dripleg is an example of its use as a heat transfer medium. No issues as far as corrosion as long as one keeps the mixture in an oxidizing state, but eroison is an issue wif sand or limestone is used as the solid media. Other meida could be used to lower the erosion potential.
"Nobody expects the Spanish Inquisition! "