Animation was full last year, but I probably got on that line "only" 2-2 1/2 hours before, I walked around the floor first, maybe went into Dreamstore, cannot remember exactly. I know I walked around and went into the Avatar exhibit, Imagineering. Animation panel was quite entertaining in 2015.
It WAS possible to do both Live Action and Parks last year, we did it. We were seated near back of Live Action, group C. We RAN. I think actually I ran, my friend is not fleet of foot. She joined me as soon as she could, maybe 5-10 minutes later. IF you try this, and I may try it again, you have to really dash. Do not stop for any reason, like bathrooms or food. Last year, we had to re-exit to outside the building, and file back into the basement holding area. Once there, you can settle in, run for food, bathrooms, etc.
Who knows what will happen this year. I am hearing that people think Live Action line will be much earlier, because of the Comic Con being scheduled so close, is expected to bump up the live action crowd. I am undecided. i was ok arriving at 4 am. But 1 am? Not sure about that. Might still go at 4 am, and if it is full, do the floor, smaller panel, and line up for parks. Ugh.
I love the big panels, but my favorites have also included small panels. Voices of the Parks (!), Monsters University, Little Mermaid ride, new Star Tours, Carsland, Pixar panels, these stand out in my mind. And the Merrie Melodies concert from last time. OUAT.
Disneyland Hotel history. I look forward to seeing the whole lineup. I would absolutely prioritize a Agents of SHIELD panel, but they go to Comic Con, not
D23. (They have never had a Marvel or Star Wars panel, that I can remember? ) Maybe they will have a Pandora panel, that would be great, too.