Disclaimer: I don't bike, although I used to occasionally commute to work via a kick scooter when I was in the mood, or when there was something wrong with the subway. Your other points notwithstanding:
> You may have to be confident/experienced/macho enough to ride among traffic and navigate big multi-lane junctions.
But not so much if they're closing large areas of the city to cars, right?
> You have to own a bike you're happy to use. [...] You have to plan out and learn a route. [...] You may have to figure out how to store your bike at both ends.
It occurs to me that this applies to cars too, and cars are an order of magnitude larger and more expensive. So it's mostly a cultural change.
> You have to be fit enough for the distance you need to go. [...] You have to be willing to shower and change at your destination, or not do so.
Would an electric bike help with this? Lower level of physical exertion = less sweating.