It was originally planned then removed from the specification. There's a workaround already available which consists in layering the same program in a multi.
The unison function *may* be re-added in V1.5 or more likely in V2.
Suggestion: make the unison dynamic. That is, you can set how many voices to stack (and a de-tune). If you play one note, all voices play it. If you play two notes, half the voices on each, etc. I've seen this on other synths (Andromeda?). It gives really thick lead lines but allows playing chords without it becoming too thick.
