Sent to your email. I also included uses of AlphaMasks/ RenderMasks for texture blending and texture shadowing.
Also, as far as changing the interface, do you know yet what changes will be necessary? If so, making as many as them as possible immediately might be better then incrementally changing the interface. I'd prefer a one-time transition than having to modify my code everytime I update. (Although I certainly understand it's not possible to anticipate every possible interface change you may need.)