If everyone is on a bike, 8ft isn’t enough

This is silly for multiple reasons

• Bike paths have significantly higher throughput than roads

• This is not a mutually elusive choice, we can have multiple modes of transport

• Rail transport & busses are more than capable of helping to reduce the load

• I never once said "everyone should be on a bike"

also now you’re going to have even bigger cities since most people will need to return to the city from living further out.

This just makes no sense. The ratio of transportation types has little effect on city density, zoning is way more of a factor. And in addition to that, car centric infrastructure takes up significantly more space than other modes. Reducing car dependence would actually free up space.