I don't see why Zero would limit it to a track-only bike. eRR is becoming less relevant, and the eSuperStock has never been truly relevant as an award. Homologation is a non-issue.
The Size 6 controller costs only a little more than the Size 4 - see
electricmotorsport, which offers the Size 4 controller for $925 and the Size 6 controller for $1195 (+$270).
The extra cost is all in programming the controller to work reliably, and then perhaps any marginal cost increase associated with a more difficult tuning process, if any.
They can then price-drop the Size 4 bikes by (say) $1000, and offer the Size 6 bikes at 2013 prices. That gets them both a slightly lower entry point - good for bringing new feet in the door - and a higher acceleration / top speed. Suppose they offer 25/98 tooth gearing as stock; 17% reduction in gear advantage, but a ~30% increase in motor torque from the bigger controller means acceleration is markedly improved, and advertised top speeds in the 115-120 mph range .. and possibly a small increase in highway range and sustained top speed.
28/132 tooth gearing options would let the S wheelie like the FX, and perhaps make it the quickest production EV in the world (~3.7s 0-60 = as fast as the Tesla Roadster Sport). Top speed and sustained top speed would both go up a little too.
Now they'd have a Size 6 bike that can out-accelerate the Empulse, outrun the Empulse on the freeway, and offer more range.. at $1000 less than the E1. Unless Brammo drops their prices as well..