That would give a little more value to Necalli's debut.
SF has Sagat
SFII-SFalpha/zero has M. Bison
SFIII has Gill
SFIV has Seth
So it would be better if SFV has a new powerful character as the boss, Necalli have a lot to be a new character among the others; the mysterious mystic killer monster story, the "V" of SFV scar on his face, and all the bosses have a superiority, Sagat was better than the others, he was at the level of Ryu and Ken, M. Bison has the Psycho Crusher, a broken move, Gill has everything and Seth has a mixed moveset, I don't like characters with a bunch of unoriginal and unrelated special moves, but Capcom corrected that in SFV. Necalli's superiority is the endless V-Gauge, the new addition to SF.
Even then, I just don't see Necalli as a Boss character. The boss character in SF must be someone whose actions affect multiple people or countries. Sagat challenges the whole world to a competition, he wanted multiple people to fight. M. Bison wanted multiple strong fighters to brainwash them and use them as an army to take over the world, Gill leaded a society that wanted to take over the world and make "harmony", Seth wanted multiple strong fighters skill to become an ultimate fighter.... and take over the world too. Necalli is not the kind of character that would affect more than one people at the time, he's like Akuma, enough power and character story to be the boss, but not the kind to be the head of a tournament, so Necalli is better as a secret boss, and Capcom knows it, so they use M. Bison as the boss.
Akuma killed him
That's another reason why we're not going to see Necalli as a boss, but well, any other boss would be murdered by murdered by Akuma, Bison actually was already killed by him, the thing is that he came back. Gill could also do that, and Seth is inmune to the Shun Goku Satsu (It stills hurts him, though).
What do you think?