Can you be drunk riding in the "driver's seat" of a level 5 autonomous self-driving car (fully autonomous no steering wheel and no pedals)?

In my state, you can be charged with a DUI if you're sitting in your car with the keys in or out of the ignition.  So hypothetically, you can be charged with DUI in a fully "autonomous car."

There will never be such a vehicle, so I'd worry about something else.  Anyway, yes.  The person "in control of the vehicle" can be arrested.  I have actually seen passengers arrested IF they are in the front seat or IF they are immediately behind the driver because they could grab the wheel.

People can and have been arrested for being drunk as a passenger because they are and can be a safety hazard. Not too common though. 

Yes you can.  But I think your insinuation that no manual control would exist is dead wrong, and if so you would then be guilty of dui.  The article says the vehicle can operate without a driver, but didn't say a driver couldn't operate the car.

no.  that is drunk driving.  so called "self-driving" cars all require the operator to maintain the ability to intervene in the car's operation at any moment should circumstances require that.  I do not foresee any state allowing what amounts to fully driverless cars within generations.

Drunk driving laws are different in every state, and I don't think anyone has written laws for self driving cars.  So it would depend on how the law is worded and how a court interprets the law.

I wouldn't risk it.