Randy from NECA has dropped two pretty huge hints about what the SDCC exclusive will be this year.
First:
https://twitter.com/NECA_TOYS/status/832920100672045056
And now from Pixel Dan's interview:
http://www.youtube.com/watch?v=jii7qUhQfWk&t=10m0s
A 30-year turtle anniversary is of course the debut of the cartoon, so I feel pretty confident that there will be a release similar to last year's arcade turtles in cartoon form. I predict they are better than the Figuarts.
If there's a villains four-pack, I bet instead of three foot soldiers it's one foot soldier or Krang plus bebop and rocksteady.