Lazav has a huge potential in all formats, but it looks like it will most likely become the basis of the Legacy Phyrexian Dreadnought deck. The plan is to play Dreadnought on turn one and sacrifice it. Then, you play Lazav on turn two and it becomes Dreadnought on turn three with 12 points of power, which can instantly attack.
Another opportunity is the EDH Commander, where the original Lazav from Return of Ravnica had its moments. Although this one requires a different approach, it will be no less exciting.