I don't have any objections to your ideas, but I don't think they warrant a codex for each legion. That could be achieved through a bit more detail in the vanilla codex. The only probelm, is where do you stop? Why just the original legions? After all, BT and CF are both successor chapters, yet they get more coverage than say Iron Hands (who are much more interesting IMO). I think that is probably because, other than their desire to 'pimp my ride' their own bodies, they adhere pretty closely to the Codex Astartes. I personally like the system of a special character unlocking unique abilities for a chapter. What I would like is much less focus on the smurfs and a codex that focus on SM in general.