And imo this is like a Noah. maybe an akuma can became a Noah (as a final form).
That's what I thought before chapter 187, where it is revealed that the original Noah were humans. Also, the Akuma obey the Earl and Noah without question. Even those Akuma that Cross was able to restructure couldn't hold out against the Earl's orders for long. However, the Level 4 that was born at HQ rebelled against the Skulls... So I personally think it is possible for Akuma to reach such a level that it could rebel against the Earl completely.
Alma, for example, did not so much obey the Earl but more like his goals aligned with what the Earl wanted, so he accepted the Dark Matter and went to town destroying the Order. The deal with Tokusa suggested that it is theoretically possible to squash/override the dark matter.
Also, I have to note that while the Noah obey and protect the Earl, they are definitely independent of him. This is based on what Cyril says when he interrogates Bookman: They listen to the Earl without question, but they do intend to act on their own when it comes to Nea, which means they are capable of rebelling. However, when wisp!Road talks to Wisely, she seemed truly terrified of the Heart and the Earl potentially getting killed, which suggests that the Noah existence is still somehow tied to that of the Earl.
Howeveeeeer............
We recently saw and heard Nea explain that the Earl feeds on souls by absorption, seemingly similar to how Akuma feed by killing. The Earl also mentioned how the Akuma are his "arms and legs" (or was it "eyes and ears"?), and Alma mentioned that Akuma are offshoots of the Earl, which is how he knew that Allen was a Noah. This suggests that there is a deeper connection between the Earl and Akuma than just toys and toy-maker. If the Earl synthesizes the Egg himself, the Akuma could literally be his... kids.