Ok, i'm not sure if you are familiar with this, but in Japanese folklore, the moon is very often associated with illusions and goin insane. I don't have non manga proof of this, but there is a little manga evidence. First of all, Aizen's zanpakutou is called, 'Kyoka Suigetsu,' meaning mirror flower, water moon. It is an old saying signifying the illusions of this world, for example there is an example of a monkey trying to reach the moon, but he can only touch the reflection on the water (reference to the 'water moon' in Aizen's zanpakutou name). Also, if you've read the manga, naruto, then you'll know that itachi's tsukiyomi (a very powerful illusion technique) is also related to the moon.
conclusion: so the conclusion is that ichigo's zanpakutou, zangetsu means moon cutter, and his attack means moon fang, heaven's destruction. so, in this case, if aizen's abilities are the moon, then that will mean ichigo will eventually create a 'moon cutter' move to defeat aizen. will this be the perfected form of getsuga tenshou, or will it be an entirely different move? i don't know
again, this is pure speculation, so you are free to pick it apart as you like.