Giving everyone the same choice in how to shoot it is fair. There is no need to mandate that everyone use the flashlight.If you are playing a game, which IDPA is, then it must be the same for everyone. So all use a flashlight or all do not.
Which I think is preferable to mandating a particular course of action in the stage description.You can force what you want with course design.
We've set up surprise stages where one will likely miss the opportunity to shoot a disappearing target if one elects to advance before tac-loading. Everyone is free to act as they wish, and pay the consequences.