Probably best to let the Inverter do what it does best, drive the motor. The "Regen" requires a special all-voltage, all-frequency AC to DC conversion, and then does "charging". The on-board charger could share some components, but these are usually not expensive parts.
Cooling a 6.6 kW charger might be the issue, but probably "too much else to do", "not really necessary", and perhaps even "it is a nice step up for a later model" have driven the decision to just use the "world-wide" 3.3 kW charger design, at least for roll-out.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle