I doubt making this implementation would provide much of an impact in our metagame, but it does complicate the definition of Species Clause. You're basically saying that some formes can be treated as "different" species, while other formes (ie Rotom-A formes) are not. The freedom to compound your team's weaknesses by doubling up on these formes is not a big enough incentive to complicate the Species clause.
Also your definition of "same typing, diff stat distribution = formes" really questions the credibility of your request. To say Latias and Latios are essentially diff formes of a same species is like saying Infernape-Blaziken-Emboar, Tauros-Miltank, Omastar-Carracosta-Kabutops, etc. are formes of same species, simply b/c they share the same typings with diff stat distributions. This is a very flawed view of species and formes.