Hi,
I wanna thank you for your amazing work! It is quite helpful and really efficient.
I think that an editor after the map generation may make your generator perfect. Yes, editing rivers and coastlines could be nice but being able to add other stuff like districts, moving the walls etc. shall be amazing . I know it is possible with a SVG editor but it is quite hard and it is only a workaround.
Well I know it may be very difficult but that's just an idea to improve your generator ;)