This whole Akuma thing is getting out of hand... With the advent of Evil Ryu and Oni SF has set a precedent: alternate timeline characters, both being possible future versions of characters in the same game. Cool, but potentially messy and confusing, how many of the same character do you really need? Esp. when the shoto chars used to be pretty much just a pallette swap of the same char anyway? But I do think there's a proper way to handle it, and your going to need two Akumas...
Like Evil Ryu, Shin Akuma/Oni is basically an amped up version of Gouki, but unlike Ryu, its a foregone conclusion that Akuma becomes Shin-Akuma, and will eventually lose his humanity entirely and become Oni, so it makes sense to me to either just consolidate Akuma/Shin-Akuma/Oni into one character, (Oni, I actually love Oni, and if he had 'Kuma's air fireball and some kind of ground teleport/Dodge he would be The Duke,) but then you lose the distinct style of Akuma, and that would be bogus because I mained Akuma for nearly a decade after SSF2Turbo...
The best thing to do would be to either split Akuma at Shin-Akuma with "Akuma" transforming into "Shin-Akuma" with V-trigger and "Shin-Akuma" transforming into Oni during the match. I actually like this solution, but I realize it's kind of dumb from a game design perspective. So what they ought to do is just straight up give us Akuma and Shin-Akuma and Oni, and whatever surprise version Akuma or Oni Capcom has been keeping secret...
But also...
They need to give us ascended versions of Gouken and Dan...
Gouken needs to achieve complete Zen emptiness, (possibly going so far as to leave the nameplate blank on the select and match screen,) and rely almost entirely on counters, techs and teleports...
And I'd love to see a new amped up Dan who's gone back to nature and managed to tap into both the Satsui-no-hado, (we know that he can muster the power, but doesn't have the skill to control it,) and the power of Emptiness. Dan has become as integral to the franchise as Ken and Ryu as far as I'm concerned. Keep him the same, or make him corrupted by Satsui-no-hado in his quest to avenge his father, or have him grow up and become what Ryu sought to become. Whatever, just don't forget Saikyo-Ryu!