According to Deadline:
Danny DeVito is negotiating to join Tim Burton’s circus in Disney’s live-action rendering of Dumbo which is casting up now. DeVito is trying to work out schedules on his Broadway turn to join Eva Green in the story of the beloved baby circus elephant with the big, floppy ears.
Deadline goes on to say that DeVito would play "Medici, the man who runs a smaller circus that gets acquired by the evil big top circus villain Vandemere" (it's sentences like these that make me realize I remember far less about Dumbo than I thought I did). Eva Green is in talks to play Colette, "a French trapeze artist who works for Vandemere" (there's another one).
Meanwhile, I'm still sitting here wondering what the hell a Tim Burton Dumbo movie is even going to look like. Personally speaking, I hope Dumbo himself is - in the grand tradition of Tim Burton design choices - both freakishly gnarled and delightfully whimsical at the same time.
Stay tuned for more on Dumbo as it becomes available.