I sent Zero an Email asking what they do with the "Upgrade" return bikes. If you do not know, Zero will let you upgrade from say a 2012 Zero S to a 2016 Zero DS where you send them your bike and they upgrade the motor, controllers and battery pack. It is cheaper than buying a new 2016. So I asked if they would sell an older set of motor/controller/battery pack so I could build it into a reverse trike. Here is the respnse and it does sound promising:
Our drive train division is working on some turnkey products that will allow guys like yourself build custom bikes. In reality, there is more to just pairing a controller and a motor together. Our complete system will include all the hardware & software preloaded and ready to go for the system to work well. We hope to have this available sometime early next year. It is still in the development stage at this time.
It does sound like we would be the perfect solution for your custom bike!
What would you be willing to spend for a system like that? The electric trike I've built has been upgraded using the same motor Zero uses in their big bikes and a 7kwh lithium battery pack. The reality of it as Zero mentions but doesn't elaborate, is the battery is the big nightmare. Judging by how their motorcycles are priced, they are charging $1000/kwh of battery (3.3 to 6.5kwh costs nearly $3k more). I built my battery for around $100/kwh with good used 18650 cells, and have a primitive BMS and simply charge it slowly to keep it balanced!