Here is a proposal for a new type fuel economy standard: every vehicle of any type may use no more than 2 gallons (or energy equivalent) of fossil fuel to go its first 100 miles. This is to say, a vehicle is required to get 50MPG for its first 100 miles, but there is no economy standard applied thereafter.
This standard can be met by light, reasonably aerodynamic vehicles with well-designed engines, incorporating useful but already-proven technologies such as start-stop, cylinder deactivation, direct injection, CVT or 7+ gear dual-clutch transmissions, variable valve lift and timing, etc. I do not believe this standard will require electrical propulsion for these vehicles. Alternatively, a weak hybrid (ex: Civic) might well suffice.
This standard will be met by mid-size vehicles using well-designed engines and one or another form of electrical propulsion, which typically raises the efficiency of a drive system by about 50%. For instance, the Prius already meets this standard, and it can reasonably be anticipated that the Ford Fusion could meet this standard with a bit more engine efficiency and a bit more battery energy (the motor is already a strong 79KW, but the pack is only 1.2KWH and cannot sustain a full supply of electrical energy to the motor for more than a few seconds).
For all other vehicles, this standard would require a well-sized motor and a meaningful battery pack that would justify plug-in charging (even if only level 1, and perhaps best if accomplished through level 1 due to level 1's ubiquity -- plain ol' outlets are everywhere and are cheap and easy to add). If after 100 miles the battery was depleted such that it no longer meaningfully contributed to the propulsion, then the mileage would no longer be the manufacturer's concern.
The reason for this proposed standard is simple: reducing fuel usage on a daily basis is more important than trying to engineer for rare long trips. For most vehicles, 100 miles would cover virtually all their daily travel. Vehicles travel different distances in their daily travels, and no matter how far a vehicle travels it has to go that first 100 miles.
This standard would encourage the manufacture of pure EVs, because the platform would already be there (simply remove the engine and add more batteries). Alternatively, another evolution of this inherent design flexibility would be to just include some additional batteries and a smaller engine (really, an electric vehicle with a range extender). In other words, manufacturers would quickly develop a modular system readily tailored to the needs of any driver.
Lastly, I believe this standard can be economically met without the development of any new technology, without seeking to greatly reduce vehicle weight and consequently possibly reducing vehicle safety, without changes in behavior, and without the simultaneous need for an electrical infrastructure (although I do encourage widespread inexpensive support of level 1 charging and the roll-out of gas-station-supported level 3 charging) (for my part, I don't get public level 2 charging: level 2 is as labor-intensive and half as expensive as level 3, but required hours instead of minutes to charge and is probably not monetize-able).