you could use the MapsMarker API to build such a system – see http://mapsmarker.com/mapsmarker-api for more infos. For a later pro release I plan to add a shortcode which allows adding maps from frontend more easily…
The possibility to add markers from frontend the same way as some extension let unregistered user submit posts from frontend would definitely bring this extension possibilities to a brand new level.
To my knowledge only the plugin twitchers give you such possibilities, you can try to see if it suits your needs
thanks for the info – will have a look!
