Based on first-principles methods, we demonstrate that it would be possible to design efficient all-full-Heusler-alloy-based spintronic devices associating Co2MnSi electrodes and nonmagnetic full-Heusler-alloy spacers selected to preserve the half-metallicity of Co2MnSi up to the interface atomic layers. We focus on the Co2MnSi/Fe2TiSi magnetic tunnel junction, compare the stability range of its different interface terminations, and show that the half-metallicity of the Fe2/MnSi-terminated interface even withstands atomic intermixing. The robustness of the half-metallicity of this interface termination is also confirmed in Co2MnSi/Fe2VAl spin valves. With such interfaces, spintronic devices could possess very high magnetoresistive properties.