So In Vol 12, Erwin Smith spoke to Levi. Right before Erwin's speech. Erwin then starts to ask Levi:
"Can you see them?"
"our comrades..."
The reader can see that he 'hallucinates' or 'imagines' that all dead soldiers start to appear around him, watching him.
We see a similar moment with Hange Zoë. In Vol 32. In "Night of The End"
Where she proposes to stop Eren
If you consider that Hange, once asked Armin, in the Raid on Libero. Hange Zoe asked Armin if he got posessed by erwin's ghost or something. This could hint to Erwin's ghost being passed onto the next Commander of the survey corps. The ideoligy of Erwin might have been passed on by previous commanders. But that wouldn't have been possible, due to Keith Shadis, not passing away but offering his position onto Erwin. This theory can be linked through the Attack On Titan afterlife, we see in the latest episode. Where Hange, once she died, was transported infront of Erwin and some different figures. The Aot Afterlife might have played a part of 'Erwin's Spirit.' Along with the paths which connect the Eldians. Erwin incredibly strong spirit might have been interacting with the paths.
There is no real evidence to this. just two similar moments.