It would be nice to have other ways to stream media as I don't use Slacker or TuneIn. I still have to rely on my phone to stream music but no access to playlists and other features.
Yes, it would be nice, but for now those are your only options. You can get playlists in Slacker if you pay for your own Slacker Premium account and log in to that from the car.
soundcloud is now much more popular, as for me if you want to listen to new, interesting music, you should look there. A lot of young, unknown artists who create profiles and upload their music. Moreover, to pump your account there is quite easy, with the help of services such as https://soundcloudgrow.com/ . After that, there is a great chance that someone will notice and appreciate your work.