As of around the start of October, my account was changed to be part of a test group for an "On Demand" feature for free users on mobile (confirmed in a Spotify support chat). I wanted to share my feedback on the changes.
The on demand feature is nice. It allows you to choose what songs to play as if you had spotify premium, but only for the premade Spotify playlsits like "Hit Rewind". It also plays an add every three choices give or take.
The feature on new playlists to show a teaser soundbyte of songs is also nice. You can press the listing for the songs on a playlist, tap a song and it will give you a small sample (without playing the song itself).
My previous playlists will only be able to be viewed in a very odd and cumbersome interface (example https://imgur.com/OmDg4IA). This only shows a portion of the songs on the playlist, and is very condensed and jumbled. New playlists you create start out like this, but you are able to tap on the songs to see a listing view like the old interface. Older playlists cannot do this, and are stuck in this weird format.
The feature similar to Pandora's Thumbs Down (a circle with a slash through it for spotify) is too close to where a person's thumb may rest on their phone and is very easy to accidentally press. Once it is pressed, the song is blacklisted to never play again without any confirmation or prompt window, and there is no way to select the song to whitelist it again (or at least not on older playlists, because there is no way to view what songs it consists of except that odd jumbled interface).
Will update with additional comments in the future.