I went back to Flecc's original analysis where he showed roughly 10 years of 98cc autocycle, followed by 10 years of motorised bikes, followed by a glut of scooters for 10 years or so, finally giving way to the car.
From this, he predicted 10 years or so for e-bikes.
But I think that we should give fuller consideration to those old vehicles and the financial situation of that time.
The Autocycle (my uncle had one) was a throw back to pre First World war motor cycles. These old motorcycles did not have gear boxes and relied on pedal assitance to get up hills. Although cheaper than proper motor cycles, autocycles were still costly.
The arrival of the cycle motor meant that a person could bolt one onto their existing bike and have a form of motorised transport. They were comparatively cheap and sold in huge numbers.
The arrival of the Lambettas and Vespas coincided with an upturn in the economy. Motor cyclists did not like them, but they appealed to motorised bike and non riders because they offered some weather protection. Also, the full 50 cc moped with a gear box was available (google NSU quickly, some had 3 gears and dual seats)
Also, you could drive around on L plates indefinitely.
Nevertheless, we are an aspirational society, and for many, the ultimate appeal was a car. Not just for its transport benefits, but as a statement that you could afford to buy one. My father had a car, but used the bus to get to work as it was much cheaper. The car was for weekends only.
Now we have a very different situation. Anyone who wants one can get a car. Because they are so ubiquitous, very few see them as a statement of social standing.
The cost of running a car, particularly a second car is becoming a burden for many.
Congestion in cities makes many car journies difficult. Bikes can be quicker in many circumstances. Bike/Bus or Bike /Train can be the best of all.
The old motorised bikes were noisy, oily and vibrated quite a bit.
E-bikes are smooth and very pleasant to ride. The simplicity of riding kit for an e-bike (helmet and cape) because of its low speed are attractors. My guess is that outside of very hilly areas, the hub motor and small battery will survive well. Once you have ridden an e-bike, going back to an unpowered bike has little or no advantage. Many on this forum comment that their e-bike feels just like an unpowered bike, and since unpowered bikes appear firmly here to stay, I must disagree with Flecc's original prediction.