I'd rather that just be behind the scenes stuff.
Here's what I'm hoping for:
TGS - we get trailers for both 2.5 and III.
D23 - We get new character render art of main and disney characters from the trailer), concept art, environment images of a Disney world (because this is a disney event), and behind-the-scenes information about the programs they're using.
D23 seems more like the informal, talk about what they've made progress with etc. TGS is more for the formal "here is footage, take it and enjoy. More information later"