Reasonably accurate predictions of spot colors solids and tints

Hi folks, I was reading about the < ICC Labs > project for v5 ICC profiles, which will feature new spectral matching. But I am confronted with real world proofing applications today where I would like to use good colorimetric predictions of spot colors mixing. Does such an application exist? To your knowledge? Ideally, I'd like to proof artwork that mix and match process and colors. Best / Roger