Super Mario War development has been declared finished and officially no longer worked on, as far as I know.
The current head developer, Two52, has stated that the next release will likely be nothing more then some bug fixes and it will be the final version of Super Mario War.
The code repository, as far as I know, is still open however. If you wish to make your own version of it or add onto it, you are free to do so. If you want to continue the actual project officially yourself, PM me and we'll see what happens. Just don't go grabbing the code and continuing it on your own and marking it as "official" just because you said so.