What do you mean by transitory period? Do you mean appearance-wise or character-wise?
While I think Akuma's story mode was good from a character development standpoint, I think they didn't explain it well. Akuma is basically granting Gen what he wants - death. Gen wasn't on the way out like he was in Alpha 2. He probably only had a few months to live at best, and Akuma granted him his final wish. Again, Akuma isn't a horrible dude. He just loveeessss fighting.
As for why he didn't kill Ryu, it's obvious - Ryu isn't done progressing. Despite finding a new mode, dude ain't ready for Akuma, and the latter is curious as to how Ryu is gonna play out. So they resolve to meet up later once Ryu is done training. It'd be a waste to kill your rival who just learned of a power that could equal your own, you know?
What's funny is Akuma said Gen gave a useless speech to prolong the inevitable and yet that's what Ryu did except Akuma left the field.
Ryu was already out. Akuma didn't kill him so the talk was useless if Ryu was stalling. Akuma was walking away. The difference between that speech and the one with Gen's is that Akuma is just being insulting and telling him to shut it so they can get to the good stuff. That fight was clearly for Gen, so Akuma is like "dude, let's finish this so I can go home and catch Desperate Housewives and you can die or something".
The biggest issue about his character is how he started. Akuma was at first possessed, then they retconned that, THEN they had to make him an asshole who kills masters and shit, but wait, he only wants a good fight? And what's this shit about him saving a kid? He spared Adon, too? They basically have to make up for previous endeavors of making him out to be evil when he really isn't.
Appearance-wise, I don't even know what happens between how he is here and how he is with 3. Is he suddenly going to "pull a Ken and get a haircut and shave before 3 hits" or something? .
Depending on how SFV deals with the canon, he'll probably just keep the power of the beast mode but refine his look. His talk with Ryu hints that he's still a human that just loves to fight under all that mess, so hopefully they'll tie that in.
Like, let's get into Goutetsu's prayer beads that were originally around Akuma's neck.
I think that's just a stylistic choice in general. You wouldn't be able to see them with his hairdo right now, so I guess that's why he wears them as they are. Once he shaves, he'll go back to donning them around his neck. I wouldn't see why they can't be adjustable, but I can see why people would take issue with the beads being on his chest.
How I'd design this Akuma in SFV would be pretty easy. Just have him wear the same gi as he wears in his new look.
I think if we saw how he transitions from here to 3, it'd help explain some of those features, but it'll either be in artbooks or in interviews. I don't dislike the mane, but it can be offputting, so I can see why people wouldn't like it in general. But at the same time, it makes sense to me with how they are treating his character. Hopefully they finish it.
But that's my opinion on the whole thing. Overall the beads turning into like some sort of sash looked like it was there to "be cool" without having any real meaning.
Maybe there's some hidden symbolism. Or maybe it's literally a rule of cool moment. It'd be nice if they went over it.