I like our current creature positioning system. It makes sure, that the cards can be read in the best possible way.It also makes the field look better, since the creatures don´t appear on one side of the field, the field would look asymmetric with your idea.
When >7 creatures are on the field, creatures overlap. With the idea to position air creatures in the top row (and so on), the overlap will happen more often.
I don´t think that your idea has chances to be implemented. It doesn´t make sense for our current game mechanics. And btw, a FFQ, which can have 7 Fireflys maximum, is kind of useless. (Or Pharaoh+8 Scarabs max.)