I have not tried this yet but I think it may help with the lannister greyjoy unbalance. I think that with this rule there will be more uncertainty about what greyjoy will do in the first moves, maybe focusing more on diplomacy rather than attacking with brutal force the lannisters leading to an early lannister defeat or more likely to a long war that only favors stark (which is already too powerful)
What do you think?
Sorry for my bad english
I don't like the change too much because with Tyrell's completely awesome hosue cards, they would totally dominate until at least a Clash of Kings come out.