The official X-Plane Twitter account has recently posted a comparison picture comparing the default Innsbruck Airport (LOWI) between X-Plane 11, and the not yet released X-Plane 12
The preview shows drastic changes between default scenery in the two sims, X-Plane 12 featuring a much more high quality rendition in almost every area. This includes the new volumetric clouds, new vegetation, revised ground textures, and more all visible in the previews.
It is unclear if all default scenery will be detailed to this level, but it is safe to assume the new sim will bring a myriad of improvements and changes from X-Plane 11.
So far, no new information release date or price wise has been shared but we can expect to see more previews in the near future. You can find more information about some of the upcoming features of X-Plane 12 in a previous article here.