As expected, Enphase is moving to a new family of plastic-enclosed inverters which utilize a new two-wire AC wiring system know as the IQ family. The specifications for the new plastic inverters roughly match those of their fifth-generation products with the exceptions that the higher-power unit supports 72-cell PV modules and they are not compatible with Engage.
The new two-wire cabling system should prove to be both cheaper and more flexible than Engage.
Finally, it appears that the new inverters and wiring system require the use of yet-another new Envoy to function properly. I assume this is due to the lack of a neutral line in the new wiring system.
I have to believe that this major chage is aimed squarely at trying to make Enphase' product offerings cost-competitive in the market. At the same time, making a full line of products which has little in common with their previous products leaves the door wide open to departures to competing technologies. While I don't think they really have a choice, it seems that Enphase will need a flawless rollout and rapid market acceptance of their new line in order to survive.