Having read about it, it seems awesome, and would "complete" reasons sytnh soundset. It has a subtractive synth, a modular synth with FM, PM and wavetable capabilities and a granlarish synth.
To complete the package it needs an additive synth. (This is a synth with the pottential for hundreds of sine wave osillators, each one modulationg each other, like Hammond Organs or Native Instruments Razorr. It would sound brilliant, and would bring out the best in the huge amounts of sound designers Reason seems to attract.
I am waiting to see an analogue moddelling synth, which I feel would never happen, but additive might be more in reach.