I really dislike the absence of DMs on Spotify. It makes the whole social aspect of Spotify seem so lacking, while music is an inherently social thing for me. I would love to use Spotify chat to work on playlists, chat about albums, etc.
I don't use Spotify, and maybe I'm just old, but I hate every platform having their own way to communicate. Especially when I want to look up something later I have to search in 4 different places and hope their search isn't terrible. There was one short period of time where Gaim/Pidgin/Adium worked.
I understand the benefits, but I feel like the main reason these are viable is because email was ruined.