It would be nice to be able to have an advanced class for J2D’s GL pipeline that allows you to make some basic shaders, the reason this class would be basic is because J2D has only 2 axis (x, y), and the reason it’s advanced is because the programmer would have to be aware of his/her limitations of the videocard.
Obviously guessing, but I think this would be seen as outside of the remit of Java 2D. I believe the attitude is that it provides an abstraction of 2D rendering and OpenGL is just a potential rendering provider.
It might be possible to an abstracted version of certain shader options and then implement them in software if its not there.
Kev