Why not include layers? Seems like another feature request that could be pursued. Not sure I know of a direct way to request a feature or to view existing and +1.
In my case it's common to include tab reveals for more information on layers and those layers have timelines that could easily be calculated to add onto the time estimate, perhaps provide base slide estimate and all slide/layer estimate. Obviously, sending learners to outside resources would need to be calculated by the designer, but with layers the data is already there in Storyline.