How can they improve the fuel economy of the next generation Pruis?

a battery sleep switch - turning on this switch when the prius is turned off will prevent or slow down the phantom drain on the batteries and extend the battery life of both the 12vdc auxillary battery and the HV battery while the Prius is kept in long term storage.
carbon fiber front and rear bumpers - lighter than plastic and more scuff and dent resistant.

 

The HV battery already comes with a 'sleep switch'. It is disconnected whenever the car is off.

You can disconnect your 12V whenever it will be dormant for a while, but getting to it is tricky without power. The biggest drain on the battery when dormant is the keyfob system which can and should be shut off.

 

All that is right except the keyfob shut off, In my 2010 there is no manual shut off.

It would be nice to have that manual shut off for those of us that want to leave the fob in the car and just take the metal key.

 

Right, in the Gen III the shutoff is automatic after some number of days, IIRC.

 

A friend developed a smartphone app (bluetooth connection to OBDII) just for this, but it used audible feedback to coach the driver on accellerator positioning. I think it is on the android app store now. I tested it with my 07 Prius awhile back.