I'd actually find it hilarious if he isn't in the Sinister 6, because that would leave Mysterio as the only original Sinister 6 member.
Technically no, Mac Gargan technically debuted in Homecoming, but "Scorpion" has yet to be seen.
I know, I know, but I have hopes.
That's fair, but I'm comparing it to Peter Parker, who, as far as we know, has the same exact story. Perhaps, they'd make a twist and use a female Goblin or a female Doc Oc (like 2099 in that one game)? That'd be interesting, I doubt Disney would let Marvel make a six-member team of heroes or villains without any female representation.