Think about the fact that, all other points aside for a minute, you believe, when granted the time and resources to add an original SF character, you believe, despite characters like Chun-Li at his disposal, Sakurai is instead going to opt to add a third shoto.
I think if you really see this as the likelier option, it's either because you've dug in your heels, or because you don't get how much bigger Chun-Li is than all remaining characters within the series.
Since the Chun Talk was starting again, I actually never got to respond to this, But I would like to give some counter arguments
I agree Chun-Li is probably bigger than all the remaining characters, but I disagree that it's by so much that she could be the only option, perhaps the more likely option, but not the only one
Characters like Guile, M.Bison, and Akuma don't have to be Downplayed to make Chun-Li look so much better. Chun-Li already has the merits. Guile, M.Bsion, and Akuma are famous/Infamous character for a variety of reasons, and I think they have enough merits to at least be considered for a Fighter spot. It seems Guile was already considered, considering he's an Assist Trophy. Now I do think Perhaps Chun-Li could have been the priority, but that doesn't mean she would automatically get the Fighter spot
Now with regards to why Akuma would ever be chosen instead of Chun-Li, considering he's another Shoto, there are some things to keep in Mind
-Akuma uses a Deadlier version of the Shoto Fighting style, and this is reflected in his Normal Attacks, plus some of the properties of his Specials
-Akuma is a boss character, and this could allow some interesting ideas or concepts to either be implemented, or new takes on the idea put in. We could see stuff like Akuma using super moves like Raging demon, or Super versions of the Hadoken, Tatsumaki, and Shoryuken without Final Smash. We could also see stuff like him being able to Transform (perhaps at will) into higher levels of power permenantly (no time Limit), or even him having better version of Universal mechanics (like his Teleport move being his dodge that has better properties than regular dodges)
Yes Akuma still does share Similarities with Ryu and Ken, but he has enough interesting idea I think that there is something there that would appeal to people looking at the DLC. I do acknowledge though that Chun-Li does have different form of Martial arts from the shotos.
I will also like to mention that one of the Chun-Li rumors was that apparently she was scrapped for "Moveset reasons". Now whether that is real or not, or if it was real, if it could be worked on some more so whatever problems are fixed, it shows that each character has their own Moveset conceptions, Merits, and different things that need to be tackled to be realized in Smash, even within the Same series.
So Ultimately, I actually do agree with Chun-Li being the more likely option on the surface for 3rd Street Fighter character just based of merits and such, but I'm not gonna count out some of the other characters