I imagine its tough knowing which model aesthetic to choose next at Zero. The market is all over the place right now.
I suspect it's really an issue of being resource-limited, as a small company.
I don't think there's a worthwhile model they can add at this point that doesn't require some kind of fairing (well, in theory, a Harley-esque cruiser, but I seriously doubt there'll be a siginficant number of buyers for it. It's a shrinking market segment, and I don't think it overlaps with people who like electrics).
It'll be interesting to see if the decision to retain 100V for the /F platform (anybody have a good name for it?) harms them in the short-to-medium range (probably more of an issue in Europe), as at this point, I don't see them launching a new higher-voltage platform for the next few years (unless sales explode,but that won't happen IMO unless at least 2-3 large motorcycle makers get fully onboard the electric wagon, and with actual motorcycles, not scooters.)