In my first post in this thread, I suggested that this game could be a stop-gap title, and that the most desired location, Japan, was being saved for a proper next-gen Horizon.
However, upon thinking further, I think I may not be entirely correct. Mexico may have been chosen, over Japan, due to increased landscape variety, thus allowing for more creative freedom, in map design, while still staying true to the look of the country they're representing. Mexico, despite not being the fan-favorite, may be the best option for a fun, more varied map, better for moving around in all the different types of vehicles that will be available. With this in mind, could FH5, if it's coming and it's in Mexico, actually be proper next-gen, not just a stop-gap? We will see.