Yes, mobile and pc users can play together if pc downgrades version from 1.3.5.3 to 1.3.0.7, and uses the mobile server.
OP asks for crossplatform between pc and xbox one though, and that's a different matter. Microsoft only allows cross platform if both uses Xbox Live for networking (Xbox Play Anywhere). Direct networking with pc outside the Xbox Live environment is currently not allowed for Xbox One. There are a few exceptions (Minecraft, Rocket League) but they use dedicated servers to serve as a bridge between the different platforms. That is obviously expensive and Re-Logic is only a small indie developer.
While they could add Xbox Live networking support to the pc, both platforms also needs to be on the same version content-wise. That won't happen for a while yet.