Dave Filoni, Kilian Plunkett and Joel Aron from the Clone Wars team return for the new 'action-filled' series for Disney XD.
Aside from that, very few details have been announced other than a Fall 2014 release date - however fans attending Celebration Europe this July will get to see a sneak peak. No art has been released by Lucasfilm - although Filoni mentions returning to Ralph McQuarrie's sublime concept art for inspiration for the series - but a few weeks ago Dave posted an image of a TIE fighter on Facebook that is more than likely for Rebels:
The timeline goes against what many expected from Lucasfilm Animation's next project, with much thought being put towards a post-Return of the Jedi era cartoon ahead of Episode VII. It raises some pretty intriguing questions though - the news post specifically mentions that:
The action-filled series is set between the events of Episode III and IV — an era spanning almost two decades never-before explored on-screen.Star Wars Rebels takes place in a time where the Empire is securing its grip on the galaxy and hunting down the last of the Jedi Knights as a fledgling rebellion against the Empire is taking shape.
Could there be a chance for an older Ahsoka Tano to make her return - assuming she survived Order 66, that is - as one of these last Jedi? After all, we never saw her story resolved...