I think SD have a very good system in place.
I think they have it so you cant unlock the light body type right away, nor the heavy, you start at medium.
Players will play with medium and like it, get used to having that much health, enjoy the weapons etc…
Then when they unlock light they will try it. And alot of people will enjoy a couple of games, but then will be annoyed that they cant take as many bullets and they have less powerful weapons, and i believe the vast majority will switch back to medium.
This is what i think will happen.
I think think the reason people think light will be so popular is because the vast majority of people think that each class has class specific weapons and havent yet grasped the concept that weapons are body type specific instead. Its a new concept and i can see why most people will have to play it to get their head around.
But because of this, most people think that the snipers and smgs etc are light only, and people like playing with snipers and smgs. Once people realise that heavys and mediums can have an assault rifle then a sniper or smg as a secondary (dont know if sniper is possible, may be for heavys) or just have a sniper as primary then they will start picking bodyweights according to how they want to play.
I think it will be pretty eavenly spread out.
I usually play all classes pretty evenly, i sometimes go through phases of one type, but i never stay exclusive to it.
I think in a match i will probably end up switching between all 3 for various situations, should be fun