This decision is ultimately not as surprising as it may seem on the surface.
What exactly this could be is up for speculation with an appearance from Deadpool again being a strong possibility.
Regardless of what exactly is shown before, be sure to be seated well before Logan starts to make sure you don’t miss it.
While some may be disappointed that a post-credits scene won’t be attached, Fox may make history by attaching some sort of tease or greeting to the beginning of the movie.