I use Spotify when I host parties. I use the built in crossfade feature to make it feel like there is a DJ. Sometimes on shuffle or a bad call will play a song that doesn't fit the current mood. I think it would be a great idea to hold the skip button for a crossfade to smoothly switch out of the song. Hold it for something like 2 seconds and it does whatever crossfade time you have set in your settings.
This would be great to go across multiple platforms as I queue up songs from my phone that play on my computer over loud speakers which is a feature I love.
Ideas for the animation would be to slow down the skip song animation to the crossfade speed.