Actually those Plastic Man shorts are brand new, but they use the designs from the pilot. In addition to the Teen Titans, Lego Batman, and Plastic Man shorts there are also going to be these series of shorts: Aardman Animations' Batman, Lauren Faust's My Super Best Friends, and Doom Patrol. The block is confirmed to only showcase the following three shows at the moment though: Green Lantern: The Animated Series, Young Justice: Invasion (The second season of the excellent new show), and Beware the Batman (This won't premiere until late next year though, and like the previous two DC shows, it'll most likely just be a sneak peak).
At some point I'm guessing they'll show some of that Blue Beetle live-action footage as well as some behind the scenes stuff for the cartoons and comics. I hope the block expands to show some of the older DC shows and movies. However, for those of you wanting their classic DC fix, Teen Titans is on Boomerang and Batman: The Animated Series and Batman Beyond are on The Hub. Most of Marvel's cartoons are on Disney XD, but a couple of the newer ones are on Nicktoons. Yeah, I follow superhero cartoons way too closely...