A behind-the-scenes trailer for the sequel was packaged with the 2001 DVD release to coincide with the movie’s 60th anniversary, but the move was ultimately cancelled by John Lasseter when he took control of the company.
The movie will likely never see the light of day, but if the live-action adaptation is a hit, perhaps elements from Dumbo II could appear in a sequel to that?
Among other things, the sequel would’ve explained some details on Dumbo’s father, Mr. Jumbo.