Important update: Gaby Falcone has deleted her tweet stating this, meaning the info was possibly incorrect or simply an Internet rumor which was passed along. This means the new series may not be called "Scooby-Doo! Guess Who?" and the picture above could be an unrelated project. Stay tuned for more updates as they come, and apologies for the mistake!
Despite the fact that "Be Cool, Scooby-Doo!" still has its entire Season 2 unaired in the US, it seems that we already have the title for the next Scooby-Doo series thanks to a tweet by Gaby Falcone. Though it is very tough to see, Scooby-Doom did some great detective work and found a script below Frank Welker, which clearly reads "Scooby-Doo! Guess Who?" A close-up of the script is shown below.
The new series will feature regulars Matthew Lillard, Frank Welker, Grey Griffin, and Kate Micucci, who is in her second series as Velma. Candi Milo, Josh Keaton, Billy West and previously announced guest Kevin Conroy are also in the photo, meaning it is possible they may appear in the series as well.
Thanks to @TheScoobyDoom for letting us know about this!