Electric bicycles (and other light electrics) are going to remake the world's cities in the next 30 years. The signs are already in place. The biggest transformational factor is the lack of exhaust allowing a lot of personal transport to be moved indoors.
Why is that useful? Who is clamouring to rebuild all the existing roads - which bikes already work on? Who is hoping to ride miles and miles in underground tunnels and pay to build them?
Underground tunnels for fast no-traffic movement of people already exist as subways, and move orders of magnitude more people, many times faster.
As always the answer is some synthesis of the many viewpoints.
Above-ground routes are much easier (thus cheaper) to adapt and change. Connecting outer-suburbs to an existing underground network is extremely difficult, it takes decades. It's hard to increase the capacity of existing networks. Not to say they aren't useful, but increasing capacity with above-ground cycle networks is much easier.
Encouraging people to cycle for shorter journeys further frees up capacity for longer trips where trains make more sense.
Roads as they are currently massively favour cars, to an unacceptable degree. I would cycle where I am if it didn't substantially increase my risk of death.
Existing roads will slowly become populated with light electrics and covered (perhaps seasonally) with no need to deal with exhaust gases. Some businesses will begin to provide indoor parking for the electrics. Some parking garages will be turned over to electrics exclusively. There will be almost no new roads or tunnels. It will be a very inexpensive, organic and practical transition.
But why will they become covered? We don't cover sidewalks or bike paths or pedestrian only areas, we don't cover parks and walkways through them, we don't cover beaches or ground level car parks, or anywhere else people walk and run and skate and bike outside. What would be the push to cover roadways - to the point where the parent poster thinks it will be a "big trend everyone should follow"?
There's tiny advantage to not being rained on, but you will already want outdoors clothing for wind chill unless your entire route end to end is covered and heated, and if you're on an electric bike or scooter doing 20+mph you'll want some kind of protective wear as well, most likely.
In Phoenix the roads are unlikely to be covered, whereas in Seattle or Buffalo they might want to cover them in winter. Either way, because of the lack of exhaust fumes, it would be financially viable to cover them whether they decide to or not.
I went on a voi (electric scooter) today. It was fun but I would probably crash about once a week, they are much more dangerous than a bicycle. The upshot is that I can leave them anywhere and take mostly the route I want. Downside is that I can't drive them as fast as they should be driven (they are legally restricted to 20km/h here, a better speed would be 30) and renting one was so expensive I could have taken the bus, if it wasn't because I try to avoid public transportation right now.
I don't see the electric scooter or bicycle replace the car, I see it can become a competitor to the bicycle.
The people I hear from are not replacing their cars with electric bicycles (mostly) they are replacing their manual bicycles, or getting one for the first time in a long time.
The people you hear from might have a been a bad sample. In the bike crazy Netherlands, where last year they bought more e-bikes than regular bikes, the most common use of e-bikes is to replace car trips of up to 15km distance. That is my personal experience as well and I was quite surprised.
