Id really like to be able to do multiple actions with one button press (I'm using a Sabre mouse). For example, I have a lock button assigned to the default configuration on my mouse. I'd like it to activate a "dormant" color scheme on the mouse. I would also like it if lighting changes could be assignments as well.
I wish I had full control over the DPI indicator light. In fact, it should be treated just like any other light on the mouse. DPI indication should be an option for any of the lights. Also, DPI indication should be able to use any of the lighting settings like pulse and shift. This would actually be solved if the assigned actions could also change the lighting settings when triggered.
Overall, there are so many things people want to do that it may be best if you focus on making the API as simple as possible. It may even be a good idea to consider making a very minimalistic IDE just for your accessories. I know I'd use it a lot. I haven't tried the API but I think I'll look into it now.