[Sven7]

You're talking about a Ruckus rated at 114mpg?

I've thought extensively about the same project. One of the problems is, when it legally tops out at 30mph and is rated for ~100mpg is it really worth trying to pursue aero?

Perhaps a custom frame like the one you posted could get you into a "kit" category and allow you to legally reach highway speeds. Looks like it's a single speed too. If you could get even two speeds and maintain 50-55mph it would be really great. I would recommend looking into some engine mods to get more power, and possibly a larger drive wheel. Lots of people mod old mopeds to get a few more hp, and with aero you could really use them properly.

LOTS of LED tail lights on the rear end could help the visibility issue. I'd put a little lighted fin right behind the headrest like the ones they have for cameras on F1 cars.