Some of these slot targeting cards have been suggested.
Meta Game
However there are two important details about this kind of an idea.
1) It is very different from effects in game (flooding has a predefined area, other cards target cards)
This means that fewer higher quality suggestions are much more appropriate than many average quality suggestions.
2) This is a vehicle idea instead of a rider idea.
A vehicle is a system that other effects can be tied to. Card, Creature, Skill, Active Skill and Activated Active Skill are all vehicles.
A rider is an effect that is not a vehicle but has to have a vehicle to be placed in. Devour is an example of a rider. However the restriction on the targets allowed is yet another vehicle.
Vehicle ideas do not make cards. Rather they are tools that can be used to make better cards for rider ideas.
In conclusion, this affecting the field is a good idea but should be limited to 6 cards (minimum for a series) or fewer and should only be used when it fits the rider ideas.
In Game
Fractal, Firefly Queen and Mitosis use a lot of creature slots but most decks do not. This means that cards like this either need to not affect a specific number of creature or affect a small number of creatures.