But I want to plug it in!

Ben,

You are asking for a full electric which still needs a lot better battery technology then we have now. With the present hybrids, the batteries usually only run the car for about a mile between recharges. The battery would need to be about 50 times larger if you wanted to charge it at home and drive it 50 miles.

Unfortunately, the plug-in conversions for the Prius got stalled by the California Air Resources Board (CARB) certifications. The 'problem' is that a gasoline engine produces a lot of pollutants until the catalytic converter heats up. This is taken into account with a pure Internal Combustion Engine (ICE) as it starts up, the catalytic converter is heated up by the exhaust, and it runs 'clean' for the rest of the trip. With a hybrid, PHEV in particular, there is the possibility of starting the engine many times during a trip. If the catalytic converter cools off too much, it could exceed CARB's pollution requirements.
We know, of course that for PHEV trips less than a few miles and below about 30 mph, there will be zero pollutants but CARB only looks at worst case situations.
Apparently, the folks making Prius PHEV conversions are going to have to let the ICE turn on whenever the catalytic converter cools down to a point, regardless of the battery state of charge.
Of course, what is needed is an electrically heated catalytic converer that can be heated just before starting the ICE.
I hope this helps clear up some of the questions regarding Prius PHEV conversions and where they are.