Well its just not practical, theres too many applications where car goes beyond human laziness and moves to necessity. But I'll tell you my theory:
You need more separation between cyclist and car. Its all about the mass of the travelling method. A car can handle a collision with another car because both of them have a lot of mass, and will absorb the impact. But a car and a person, or a car and a bike colliding wouldn't end so well. At the same time two bicycles can collide with relatively little pain because they are both of similar mass. Same goes with pedestrians -- isn't that why for a hundred years humans have chosen to build separate footpaths instead of 'foot lanes'. Well since a bicycle and a person would fair about the same against a car, the theory goes that bicycles should deserve their own separated bicyclepath with a nature strip separating them from cars.
So the ideal situation is that every road will be converted into 3 parts consisting of sidewalk cyclepath and drivepath if you accept my created names. Since the construction of modern suburbs and cities is already so developed that is unlikely to happen without a major change in thinking. But bigger changes have been made, and little sparks of light are always being shone from cities like Bogota etc. In the end we are only dealing with concrete and tar, that stuff is bloody tough but with enough money and willpower it can be moved.
The most important thing I think is to have a new breed of simple cheap bicycles that would allow a generation of kids to see bikes for their true beauty and not as a flashy suspension gimick that can only but discourage bike use.
Thats the world I hope for. Singlespeeds and fixxies are making a comeback i tell you, a very slow one of course but i think in a few years all the major brands will have a singlespeed and a fixed gear with brake in their range.