How could this work? There are a limited number of players who can perform at the ML level, so options are already limited. If players are not 'hot' as you say what do you do with them? Bench them, cut them, send them down to the minors? You can't send everyone down so it's either benching or cutting, and I would guess it would have to be cutting the player since the roster can only have, what, 25 players? What criteria wouold be used to determine if a player is hot or not, and are you talking only offense in this scenario? What if a player is average at the plate but a stud defensively?
This sounds like a nightmare. Who would want to play for an organization that is going to release you or send you down to AAA if you happen to have a couple bad weeks? The team would also need to have a surplus of talent in the minors just waiting to be called up in case a player wasn't performing and I don't know of a single team that has a farm system like that.