They could try a touring Zero with 20+ kWh battery? OFC it would be heavy, but it would be for touring.
Price would increase to 25000$++ probably.
The question is where they put the weight. Lets say they packed in two of the 4 module units side by side (yes it would be a wide bike) it would likely not be hard to pick up and it would feel a lot lighter than if they packed the weight on high.
20 kWh might be achieved if they modify their current box shape for the battery, to accommodate leg room and weight distribution. I don't see a wider rectangular box making sense in its current form; that would make drag reduction even more difficult. Simultaneously, once they commit to a fairing, the product design would have to focus on maintaining (or improving) battery and motor ventilation.
A range-boosting fairing and a strong L2/L3 charging solution would top my wish list, anyway, and would be more effective at increasing the bike's usefulness.
Of course, this is all speculation and it sounds like Zero has locked in a design that they're happy with, which is good because that gives them a year to test it and keep costs reasonable. I would definitely bet against a battery chemistry change.