A new concept for the design of diagnostics for fusion devices is introduced. The concept is based on the combination of sets of different diagnostics to an integrated meta-diagnostic. The approach applies methods from Bayesian experimental design and allows for quantitative assessments of differing meta-diagnostics. A specific example is the combination of interferometry and Thomson scattering data to determine the capabilities of the proposed method. The approach also determines the minimum sets of diagnostics required to determine physics quantities with a given accuracy. This is relevant for the control of reactor-relevant scenarios such as with DEMO.