I think that countries are slowly moving away from physical visas and stamps, and more toward electronic record keeping. Maybe eventually passports will be in ID card format, but that can't happen until ALL countries of the world have successfully completed the transition. Maybe once the majority of countries have done so, an ID card passport will become the norm, and issuing authorities will provide a passport booklet only upon request for those who need one. I don't anticipate this happening within our lifetimes, but who knows.