I’m just speculating, but I think they would need to re-write their animation module to support deformtions of models that hi res, but there was no mention of that in the demo video. I suspect character models may still need to be the same resolution as they are now, but static meshes will support unlimited resolution. It would be awesome however if animated character models could be unlimited too though - maybe they can figure that out by next year.
As for texturing, I think you will still need to UV and texture your zbrush models rather than exporting polypainted assets as they mentioned something about assets with up to 8K textures, I think you would just have unlimited textures? I think the point about Zbrush models was more that instead of creating lowres models and baking normals, you could just use the original hi res versions.