They don't have anything to change to allow us to play with 5 or 6 characters especially if mercenaries are planned.
What do you mean here? I don't think mercenaries will enable party sizes of 5 or 6; they'll just replace one of your 4 party slots.
Not very understandable

I meant that they don't have too add creatures or rebalance the game AND that they don't have to add more companions (a party of 6 with only 8 companions would really reduce the "party builds" possibilities, but if we have mercenaries possibilities are unlimited).