Vanguard

I think with Izanagis previous experience and role in the Zero Division along with his accomplished background, personality and general desire to protect the peace make him a good candidate for the position. With the duties of the Zero Division being changed, he'd be more suited in a position where he can directly influence the protection of the earth since at this point in time both the Soul King and the Gotei 13 are in a stable position where as the Earth receives new threats on daily bases. He's range of powers would allow him to keep a watch over the whole of the planet and with his distinct tracking abilities he would be able to detect threats in almost no time and address them appropriately. Similarly, since he was the Wisdom of the Spell and one who selected/nominated new members who were to be appointed to the Zero Division it makes him a good judge of character and a good person to recruit fresh members to the Vanguard.

I believe he's previous Position as 5th Division Captain in his early days and most recently the Wisdom of the Spell of the Zero Division.

He's tier 0-3, however I believe he's strong and influential enough to handle the position. If you review his personality, he's both a kind and caring individual and seeks to maintain peace, being the Acting Head of the Vanguard would allow him to protect the Earth it self and all who reside on it.