the built in filters has some settings, like motion blur has amount. but it' cant be assign with logic bricks.
now a custom filter, can it read a value somehow (python code wont work? or would it... like own["blur_amount"] ? )
the shaders is C code it looks like, and doesn't need to have .py extension AFAIK.
anyways, this would be so awesome, also for built in filters. so we can enable/disable and maybe script with python the transition.