I live in Puerto Vallarta, where this "pilot" program is being tested.

No FMM card needed upon entry for tourists. One's passport is stamped and the INM agent writes the date (dd/mm/yy format) in the passport. At departure, the airline agent checks the date in your passport.

No news on what happens if one overstays their date, speculation is INM is called and they deal with the situation.

As a Permanent Resident, I will have my passport stamped "entrada" upon entering, "salida" when departing.

As INM nationwide is aware of this program, (in a situation mentioned above re:flying out of a different airport), other airports will recognize and honor the date stamped in tourists' passports. Once any bugs are worked out at these pilot airports, the system will be nationwide.