Not sure if this has been said, but I think the most reasonable theory on Amon’s identity is gonna be said on this post.
As every ATLA fan remembers, Azula killed Avatar Aang with lightning at the end of Book 2: Earth. When the Avatar dies, a new one is reincarnated in the cycle; this being Amon. HOWEVER (where the mind-blown status comes in), because Katara revived Aang so soon with the Northern Water Tribe Spirit Oasis Water, this caused Amon to maintain all Avatar qualities EXCEPT the ability to bend. One of the many qualities Amon may wield include his ability to energy bend (even though Aang didn’t learn how to until Sozin’s Comet).
Another piece of evidence to support this conclusion is how Avatar Korra hasn’t at all been able to establish contact with the Spirit World (or even Avatar Aang). Quote on Quote “It’s not that I have ignored it, it just doesn’t come as easy to me.” Ignorance is bliss on this one because Korra may not understand that the past may be the reason why she hasn’t been able to connect with the spirit world and be able to have some trace of airbending in her (seeing as how she could utilize water, earth, and fire but not air because Aang originally was an airbender-born Avatar).
There could be many holes and flaws to this theory, but i believe this is the most authentic and COULD BE CANON*. ;3