As of moving tests away from src directory, I am not sure if this is a good idea. I see source distribution containing all of the code, including demos.
It already does not contain junit tests. What with demos which need considerable resources, like textures, sounds, movies for animated textures etc ? IMHO, it would be more logical to put code and resources for given demo together in separate dir.
As far as ant is concerned, it is useful for command-line build, but it can be not so obvious for IDEs, which will for example rebuild all demos for rebuild all - it is a lot easier to not add another directory to source path then to remove one package from it