@Riot: Does Ragnaros give you any ideas for future Champions?
Brand might fill in the set-the-world-on-fire niche, but Ragnaros's gameplay is considerably different, especially his Molten Core mechanic. Before you say that Azir does Molten Core, no, Azir doesn't BECOME the turret; he just creates one.
Adding in a Molten Core mechanic (in all but name) on a future Champion, IMO, would be so freaking sweet. Just imagine growing to titanic size and being able to smash apart your puny enemies as they try to fight under your turret or turret ruin.