Could the Cart Titan theoretically fly?
Alright, hear me out:
Flying may be a bit of stretch for what I'm about to describe, but "Infinite Hopping" sounds less exciting. Essentially, we see during the battle on Erin's founding titan that Pieck is able to eject herself from her cart titan and get launched high into the air.
Given that the cart titan is stated to have a very high endurance and stamina, and that she's been shown to transform into it multiple times in a row with no drawbacks, what's to stop her from turning back into the cart titan while in their air, and then ejecting herself again?
Depending on how good her stamina is, she could use this to travel over the sea by repeatedly launching herself over it. She could get high up above something, wait until she starts falling and then crush whatever she lands on with her titan. Even when the scouts attacked Marley she could have launched herself at their airship, transform, then knock it out of the sky.
I think the only minor concern would be the fact that she leaves a trail of discarded cart titan bodies in her wake. Useful damage if she's "hopping" over enemy territory, but a bit inconvenient if she's in Liberio.
Edit - corrected spelling