http://www.boeing.com/news/frontiers/archive/2004/july/ts_sf7a.html

A precursor to fuel cell/turbine aircraft engines?  The turbofan engine would be part electric motor and part turbine.  Also opening up the possibility of using batteries or ultracapacitors to plugin the aircraft before a flight, producing even greater mileage gains for air travel.

Battery and ultracapacitor energy storage are theoretically approaching the energy density of liquid fuel.  If/when they get close enough, hybrid plugin airliners will be possible.

This backup power device pictured in the boeing article could also make any electric car a serial plugin hybrid, just what we need to halt GHG global climate disaster.  But will it ever be mass produced?  Not with the auto companies now in control.  Too bad.