As a former Disney employee and someone who's kept up with internal politics, even though his contract was up at the end of next year this feels sudden and not in line with how Disney tends to do things. Disney has quite a number of disparate businesses, from theme parks to streaming services to movies. Chapek is a business guy that has done consumer products and parks (parts of the business that aren't huge growth areas), and hasn't even been president of parks for that long.
He has no experience on the creative side. Usually the future CEO is appointed to a COO/President role in order to help them learn the parts of the business they don't have experience in. It also helps vet if they'll be capable of leading all those business heads, which is how they determined not to go with Tom Staggs after he was made COO. Not doing this is pretty irregular, especially with all the shakeup that occurred with Fox. They're still working through a lot of that.
Similarly, I don't buy the story that Iger is moving into a creative leadership role. It's true there's been a vacuum there since Lasseter left, but unless there's long term tenure planned, Iger won't be very influential. Anyone who's worked at a large company knows that no one listens to the guy whose only responsibility is to have creative ideas if they have no other real responsibility and will be out in a few months. Iger put himself into a meaningless, insignificant role, and no one has satisfactorily explained why.
I don't think there's a scandal. If there was, the narrative around his departure would be different and he wouldn't be sticking out to the end of his contract. He wouldn't still be chairman of the board. I've heard a rumor the board is upset about Star Wars, but Q1 2020 was pretty solid and Mandalorian was well received. I'm actually worried he's sick, though I hope not because I admire him a lot.
Regardless, I do feel like there's another shoe. I guess we'll have to wait to find out what it is.