Gladiator is the current Majestor of the Shi'ar Imperium. However, he is not of Shi'ar royalty. He is a Strontian. First Vulcan, a human, tried to take over the Empire and succeeded. Now Gladiator, another non-Shi'ar alien is sitting on the throne. I can't help but think that some elements within the Empire would rather have a Shi'ar of royal blood as their Majestor/Majestrix. Besides, Gladiator seems to dislike his position as Emperor and would rather return to leading the Imperial Guard. So who should be the rightful ruler of the Shi'ar?
The original royal Neramani line of succession was in this order: Deathbird, D'ken and Lilandra. All of whom are either deceased or out of commision.
Deathbird is currently in a coma. However, some of her offspring are eligible for the throne. Black Light and White Noise are supposed children of Deathbird. However, they choose to serve on the Imperial Guard. Black Light recently perished in Realm of Kings. We know Lifeguard is making a return sometime soon, so it seems as if she may be next in line in the order of succession. I propose a new Shi'ar civil war between the various factions vying for the throne between Deathbird's heirs (Lifeguard, Slipstream), D'Ken's heir (Adam-X), and Gladiator's heir (Kid Gladiator) and whoever else I might have missed.