A mechanic can be interesting on paper and still have nothing useful to do in a particular room.
Fluxion is an idea being explored during Fathom's development. Broadly, it concerns changing the state or behavior of parts of the environment, creating possibilities around movement, access, and spatial relationships. It is not a finalized feature, and the current demo direction does not depend on it.
That uncertainty is important. A mechanic should earn the space it occupies in the game.
Start witH sometHing wortH doing
The temptation with an unusual system is to design demonstrations of it. Build a room where the new ability is required, place the relevant object in front of the player, and let the mechanic explain itself.
That can teach a control. It doesn't necessarily create an interesting decision.
For Fathom, the more useful starting point is an intention. The player wants to reach something, move something, or understand what happened. Then comes the question: does Fluxion give them a satisfying way to act on that intention?
If an ordinary control or a character ability does the job more clearly, that is worth taking seriously.
A sTrange result still needs a readable cause
Changing the rules of an environment asks a lot of the player. They need to recognize what they can affect, understand the result, and use that knowledge somewhere else.
There is room for surprise in that process. There also needs to be enough consistency for an experiment to teach something. Otherwise, each new interaction becomes another exception to memorize.
A useful test would compare the same problem with and without Fluxion. Does the system create a new approach? Does it encourage observation? Can the player predict a consequence after seeing it once? Does using it feel more interesting than simply operating the machinery already in the room?