The inevitable consequence would be that, just like school exams, the test will be made easier, the testing less severe to make sure the majority still pass.
It would be as unacceptable to have maybe hundreds of thousands of ex-motorists unable to drive as it is to have hundreds of thousands of youngsters without qualifications. And as far as the motorist goes, probably completely impractical, as the public transport network would be unable to cope with the extra demand and the infrastructure investment would be colossal to meet the needs.