I just think it would be a very hard sell to the consumer, even modular like that you are probably talking $200-$300 each time, and it would make it tougher on Sony's first party Devs, if you want that kind of modular that's what PC is for. I think the Pro route is the best option half way through the gen, it's not a must have but good upgrade for those that can afford it (or, as mentioned, sell the base model to part fund the pro)