The Instituto Nacional de Migración, or the Immigration department of Mexico is becoming more strict when it comes to visa rules. Immigration officers will be less flexible when it comes to the FMM or tourist visa.
Was it rather easy to hop in and out of Mexico on an FMM, nowadays Immigration officers will look at the date of your return ticket date and your hotel booking. When crossing land borders you might have to explain in more detail about your stay in Mexico, up to a point where it convinces the INM officer to get you a tourist visa for 180 days.
Mostly you will get a visa that covers your stay since Immigration considers tourists to be only in the country for a week or 3.
Snowbirds coming to Mexico will be questioned about their stay. If you own a house or have a long-term lease you will be no longer permitted to enter on an FMM. You will have to apply for a temporary or permanent resident permit depending on your age.
Are you a regular visitor of Mexico on a tourist visa? Beware that you may face a surprise at the border crossing. They might not allow you back in or allow you with the advice to apply for a resident permit next time. Especially if your last visit is less than a year ago.
A quick visa run, very popular with digital nomads will not be so easy anymore. Although we all know land borders have different checks from airports. But the idea of leaving for a quick visit to Belize and reentering to refresh your FMM not allowed in and not having all your stuff with you would be worrisome to me.
The Immigration office is doing a quick catch-up with past data, combining dossiers and scanning old documents to update the files. The idea is that at a border an Immigration officer should be able to see your travels in and out of Mexico as well as your registered address in one mouse-click.
Long story short, depending on your travel behavior, intended stay, and age you will be allowed to enter on a 180 days visa but only valid for the duration of your stay. And/or you will be advised to apply in your home country for a resident permit.