Fort Zancudo in GTA V was both a content location and a wanted-level escalator. Leonida's equivalent would be a meaningful piece of the map. We don't know if it has one.
Florida's real military presence
Florida has multiple military installations - Eglin, Tyndall, Homestead, MacDill. A Leonida analogue is plausible if Rockstar wants the gameplay it enables. Speculative.
Trailer footage at the time of writing doesn't show a clearly identified military base.