Olaf should have a rage mechanic instead of mana
instead of mana i would think Olaf would be better with the rage mechanic Gnar has as in he would get a boost to his power for a short time. Of course if they replace his mana with this mechanic i would assume they would make his q cd a fixed amount along with a change to his r but keeping his cc immunity.
And in my opinion it would fit his lore and his title "Berserker"