Upgrade path, yep. I'm offering first gen customers 40% off the new hardware. The intention is you'd move the existing engine/ESC into the new gearbox (it's easy or send it to me and I'll do it for super cheap). That $300 discount can be applied to a brand new kit as well. The upgrade would include new gearbox, motor freewheel+adapter, mounting hardware, chain tensioner, BB spindle and spider (since the chainline moved slightly). Upgrades for the 3210 engine are $495, 3220 upgrade is $545.
Overall the kit is same as before, throttle input to the CA which outputs digital pulse to ESC based on battery shunt measurement. CA included in the kit. I can omit any component from the kit people already have to save a little bit.
The spring tensioner is an 8mm diameter shoulders screw with M6 threads, so it could be used on the old mounting plates. The plates are aluminum so drilling and tapping is easy (could use a bolt on the backside instead of tapping the plate). The spring will need a small (1/16") hole drilled as well. I'll sell these individually but you'll have to line them up and install them yourself, $20. I could quickly alter the length of the arm as well, right now it's 40mm center of pivot to center of jockey wheel.
Spider/chanrings are super simple. It's difficult to get a good picture.
The mounting plate sits flush against the outside face of the BB shell, it's 6.35mm thick (1/4"). Center of derailleur chainring on the inner position is 5.5mm off the face of the plate (12mm outboard of BB face, about where it should be). The spider is on the inside of the FW flange, derailleur ring on the inside of the spider, motor chainring on the outside, RaceFace Bashguard chainring bolts are used (they're long, the sleeve passes from one chainring to the other). The new position of the motor chain is 14mm outboard of the mounting plate (20mm outboard of BB face). 5mm of BB spacer is used between the FW and crank arm to move the FW farther inboard.
Altering the arragement of the spider/chainrings is easy (mount spider on outside of flange, remove BB spacers, etc). Additionally, it's sorta tough to see with the raw aluminum, but the entire drive unit can be shifted left (non-chain side) a few mm's if your frame is wider than 73mm:
If the spacers on the motor side were removed so the plates would be flush with the drive housing, they'd be 73mm apart. There is space between the crank and motor to accomodate a little shift. In the pic below you can also see the gold heat sink sandwiching the ESC against the mounting plate. Many fancy frames have a wide attachment to the BB shell, similar to this 951, so the ESC can't protrude inboard of the BB face very far or at all. A few spacers between the ESC and mounting plate shift the ESC/heat sinks outboard until the frame is cleared. The kit will come with nice spacers, not the cheap-o washers in the pic.
The motor freewheel adapter will be made a bit shorter so it stays within the FW. We could also easily use the M6 screw in the center for a chain guard.