I personally hope ebikes come to fill a space between cars and bikes. My dream ebike does 35mph+ for 40mi+ with 50-100w of human input and has some cargo capacity and probably an extra seat. My household has a car (prius-c) and a converted van for longer trips / cargo moving. For me, this would allow me to ditch my car which is primarily used in the city. Though a bike like this would be pretty competent on surface streets mixing with automotive traffic, I would still probably need _some_ infrastructure to make it work well. Secured ground-level storage & parking near stores and points of interest, and streets with appropriate speed limits (<45mph).
The climate where I live is mild costal, but I believe this is possible even in more extreme continental climates with spikes, etc. Clothing tech has made staying dry & warm not too hard.
I have looked at the Twike but it's just an impractical device. Way too expensive & trying too hard to be a car.
Some corrections: - Freewheels don't preclude regen - You'll always need brakes - Some folks need better than 15-20mph ;-)