I always got some interest in tricycles. I'd rather get a traditional one for leisure.
But those reverse-trikes such as the T-Rex and the Can-Am Spyder, are a good base for a hypermiling-oriented project. Also due to the absence of a differential they have a fairly easy maintenance and less technical complexity. Considering power and torque ratings I'd consider a BMW motorcycle flat-twin with its shaft drive as the best setup, since some models have the reverse "gear" all-electric, which could be a good start for a hybrid project...