There is no requirement to convert cars built to run on R134a to use this later refrigerant, and may legally be recharged with R134a for the foreseeable future.
The only cars which must use this new refrigerant as at November 2013 are those completely re-designed since 2011 but by 2017 every new car must use this new refrigerant and if originally built for R1234yf must only ever be recharged with that refrigerant, by law.