I believe they can and will next week or 2 weeks from now. Remember, we just had Episode 3 on the Toonami block Weekend stream!
Also, JoJo's Part 1 didn't get its first marathon (of Episodes 1-5) until the week before its Christmas Eve on-air marathon (of Episodes 5-10)!
As for a Stardust Crusaders on-air marathon? I would say Saturday before Halloween (October 28th), but how far back it would go is a mystery. If they get to use all of Toonami's timeslots, then we're talking 3-12, but that 3:30 AM timeslot might be different, so I'd say 4-12.
Edit regarding Shippuden: It's actually 161-165 right now (completely skipping the 150s, apparently)...or WAS before 8 PM-ish. Now the Toonami stream is playing...Robot Chicken!?
Nope, Pre-Flight. But it's still really weird that it switched to the Robot Chicken marathon when it got close to 8. Should be back to 161 about 9:30.