After all this time my historical senses were tingling, people discussing mesoamerican and Mexican cultures as civ candidates...
To add my two cents
1-Santa Anna would be the absolutely worst choice for a Mexican civ leader, as other have mentioned, he was overthrowned several times, and is despised to this day. As a fun trivia, the Mexican hymn
had several lines dedicated to him, Its a punishable crime to sings those lines in any official capacity...so yeah we kind of don't like the dude. There's more Mexican history besides El Alamo, but I get why that's the first person to come to mind to so many people.
2- Other more interesting leaders could include Benito Juarez, Porfirio Diaz (a younger Diaz could avoid any controversy) or a founding father like Vicente Guerrero, heck if you go the Gandhi route and choose from famous figures that weren't president you could add Emiliano Zapata, gotta admit I'd love to see him animated.
3- I agree in that the rurales were actually a repressive force used under the Diaz dictatorship, I think Lanceros de Jalisco could work very well. However if you wanted to add something with more revolutionary flavour, Soldaderas could be an option. There were full female regiments that fought during the revolution, hard to get a more iconic look.
as for the whole Teotihuacan vs Toltec discussion, I've long talked here about my dissapointment with Teotihuacan not being a CS, along with so many other deserving mesoamerican cities. However I'd rather see mesoamerican civilizations we know more about and cover all the bases (leader pool, many cities, unique and alive language, well documented) so, for example, Purepecha, Zapotec, Mixtec. Or even alternate leaders for existing civs , both Aztecs and Mayans could easily have one.
All that said, I do believe the Aztecs are due for a leader that embraced the Toltec ideal (Nezahualcoyotl), but Firaxis will never do a leader other than Monty it seems.