We have learned from freeway expansion projects that constant-factor improvements in capacity induce growth in utilization until we return to an equilibrium level of congestion. We're in the early stages of this process for bicycles, so the pain is low for now, as it was when early adopters had the brand-new interstate highways all to themselves. As it was, more recently, when hybrids were allowed in the Bay Bridge flyover lane. What happened? Everybody got a Prius.
For environmental, health, and inclusivity reasons (constant factor improvements in transportation capacity do, after all, mean constant factor improvements in access to cities) it may be preferable to have gridlock in bicycles rather than gridlock in private cars.
But don't think for a second that we can grow sprawling mega-regions indefinitely without gridlock.
The limit on growing a mega-region with bicycles is simply that bicycles' limited speed makes them impractical for travel of more than 10 miles for most people.
But Tokyo's 38M-citizen megaregion of train stations accessed by pedestrians and cyclists[0] is probably the best-scaled megaregion yet to exist.
For environmental, health, and inclusivity reasons (constant factor improvements in transportation capacity do, after all, mean constant factor improvements in access to cities) it may be preferable to have gridlock in bicycles rather than gridlock in private cars.
But don't think for a second that we can grow sprawling mega-regions indefinitely without gridlock.