I think you have to be realistic.
Unless you have extreme closeups all the time 8k or even 4k textures could be a waste of resources. It also depends on your delivery requirements. I use 1920x1080, which is what most film festivals I submit to require.
It is animation after all, so you have to think what that very high resolution brings to your story. With digital imagery being too crisp often, people try to emulate the certain fuzziness found in film.
That said, if a texture atlas is used for a prop (many props by third-party developers are like that) then high resolution makes sense because the parts may only use small segment of that. So I have been upscaling such textures, because the originals were inadequate, especially for props that have text on them.
I hope this makes sense...:unsure: