I know there is a post on limit breaks but this suggestion is slightly different , im not sure regimes or weapon skills in game but i could suggest this system instead.
Have a active time battle bar like how it works in final fantasy 7 but this bar not used for basic attacks but for skill combinations or maybe even the system they use in ff13 the paradigm shift but use an atb bar to set a timer on it.
This could be an added layer on top of the new changes of battle system they bringing out soon.