This is an idea previously posted which captured the essence of how crossfade should work with most songs (Specifically, my idea relates to solution #2 in this post) :
In other words the idea is that there's an inherent need for proper transitioning between songs in a playlist. If the user has the ability to customize the crossfade on a 'per song basis' they would necessarily have the ability to control the flow of a playlist.
Here's to creating a richer Spotify experience.
Updated on 2020-05-11
Your idea was submitted a while ago and unfortunately didn't receive the amount of kudos needed to stay active in the ideas board (100 Kudos per year).
In order to keep the Ideas Exchange clearer I'll close this idea for now, but this doesn't mean Spotify rejected this idea.
If you think this is an idea which needs to be implemented, you're welcome to post it in a slightly different form 🙂
Have a nice day!