I've just released an add-on for Advanced Custom Fields that adds the Mapbox geoJSON field-type. The field has a graphical interface for editing geoJSON-data, drawing PolyLines, Polygons, Rectangles as well as adding markers directly on a map. The plugin is available in the WordPress plugin directory.
The data that the field produces is saved and retrieved as a string of geoJSON-formatted data. Read more about this data-format over at geojson.org.
Below is an example where I've used all of the current features of the field to create a
FeatureCollection with four