Astiga Web Editing Playlists - Multiselect
When creating playlists on the web, since most users would be using a mouse or touchpad, I think it would be very convenient to allow selection of multiple tracks in the playlist so that large groups of tracks can easily be reordered, deleted, etc.
This may also be useful for mobile if there is a way to manage when the user is looking to select multiple songs. But I say this mainly for web. [Edit: I now realize this is already possible on mobile with the long hold]