While we're are assured that Marvel will be announcing a slew of titles today at Comic-Con. One is already being confirmed by a screenwriter from Marvel's writers program. Nicole Perlman, who originally wrote the first draft of Guardians of The Galaxy, confirmed to TheWrap in a video interview that James Gunn would be returning to write-direct the sequel. Perlman also wrote an updated script for a solo Black Widow film (and is rumored/unconfirmed to be involved with the Ms Marvel script as well).
Gunn went even further while speaking with FilmDivider and revealed what we could see in the next installment, which hinted to focusing on Peter Quill's father and his role as a member of an intergalactic royal family.
Not to mention seeing more of the world of Yondu and the Ravagers (group of thieves/smugglers).