In 1990, a typical V8 produced 220HP or less HP, and ran under 20 mpg highway. Today, most all V8's are over 300HP, and even the pickups get over 20mpg, with some cars getting over 30mpg. To put it in perspective, the four bangers should now have 150HP and get 75+ mpg.
Back on subject, I honestly believe there is a solid market for a narrow single seater with super high economy IF:
Configure it with optional add-on modules. A storage module, a two passenger module, a supplemental 50HP power module.
Like a cross between a railroad car and a trailer, the modules could be easily plugged into the control module to form a train, and the vehicle be configured to perform multiple tasks.
People Hauler - Add 2 passenger modules and a power module if in mountainous areas.
Delivery wagon - Add one or more storage modules and a power module if necessary.
Commuter - Control module only.
High Speed Commuter - Control module + power module.