Looks like the rumors were true. We now have confirmation that Obi-Wan Kenobi will be appearing in Star Wars Rebels in holographic form. In the above clip, you can see Ezra Bridger watch a hologram with Obi-Wan saying "may the Force be with you" (translated from French).
If I had to guess, I would say the hologram is the message that Obi-Wan recorded in Star Wars Episode III: Revenge of the Sith, warning all Jedi to stay away from Coruscant. It's the likeliest reason why Kanan Jarrus (presumably) would have a message from Obi-Wan, especially when we know that Kanan's past is tied to Order 66.
Are you excited to see Obi-Wan return? Let us know in the comments below!