This is totally not confirmed (but seems likely), but this French streaming website has listed that Jojo Part 4 will have 39 episodes!!
And that means enough Jojo to last till....Christmas???
To compare to previous seasons,
Someone did the math: Part 1: Phantom Blood: 44 chapters, 9 episodes. 4.88 chapters per episode. Part 2: Battle Tendency: 69 chapters, 17 episodes. 4.05 chapters per episode. Part 3: Stardust Crusaders: 152 chapters, 48 episodes 3.16 chapters per episode. Part 4: Diamond is Unbreakable: 174 chapters, 39 episodes. 4.46 chapters per episode.
3 full cours of Jojo, probably coming your way!
and its probably going to be a weekly schedule unless something very strange is up!