With the multitude of effects that we have that require adult pets, I really don't see any downside to this.
Huge support.
It would only make sense - instead of either trying to find someone who is willing to zap pets, or waiting an entire month to put an effect on a creatu... We put some more back into circulation. Even if it's just for a very limited amount of time and they are scarce.
Plus then more people would be inclined to give effects to their pets so we can utilize the beautiful artwork I'm sure the artists worked hard for!
/sorry I'm rambling/