Most ebikes use a hybrid tire, so not exactly an MTB tire, but close. Most ebikes use a flat handlebar, without the drops. What's the difference in speed? At 400 watts, the basic online bike computer says 4-5 mph.
I 'drop' to my forearms all the time, on a flat bar. I'm sure you are aware of a few bikes with drop bars. Flat bars seem appropriate for most e-bikers from what I see on the road everyday. I'm passing all but one e-bike, a recumbent. -S
Dillenger had a Kickstarter with a bike with drops, front wheel hub motor. Cheap, and the bike shown was just a bike they would convert later on. No funding.
I've tried to find an aero position and it doesn't work, at all. I like the drop position on my road bike.
I could see designing a lightly powered road bike that was just the standard road bike. Small battery. The Prodeco Titanio is interesting.