First of all, one of the most important goals of Embedded Wizard is the aspect of platform independence. This means, that one and the same GUI application can be run on a target with a simple 2D accelerator, or on a target with OpenGL ES 2.0 or even on a target which does not have any graphics acceleration at all.
The Platform Package concept is not intended to extend the set of graphical operations with new operations. With Embedded Wizard our main intension was to provide a platform independent graphical system with a fix constant set graphical operations. Accordingly, the OpenGL ES 2.0 Platform Package comes with a set of shaders optimized for the required graphical operations. An extension would mean, that the new graphical operation should be implemented in the Graphics Engine and be routed to the Mosaic library. Beside the complexity, the platform independence is lost in such case!
However, you could implement your own vertex and fragment shader code and your own Open GL code, in order to draw into your private GL framebuffer. This framebuffer can co-exist on the screen or it can serve as a texture for Embedded Wizard.