Color scheme and raid theming is generally more important than the race of the boss so long as the fights are visually different enough. Having the raids be yet more underground caves is a bigger risk, but we can expect a naturalistic look for 10.2's raid and for 10.3 it can conceivably be anywhere though I expect some kind of Titan facility, even if that'd be a retread on much that came before. Fyrakk as a orange and purple fire-focused baddie that's a lot about dynamism is distinct enough from a humanoid then mutated Iridikron, especially given that the bosses up to them ought to be fairly distinct.