The Playlist is a very special collection to base a Radio on, unlike Song, Artist or Album, since none of these represent a personal music choice the way a Playlist do. The Playlist Radio is therefore unique among Radios in Spotify, and it's removal from the Android app took away a combination of personalization, situation and variation that no other option provides.
It has been there, and should be easy to bring back. I'm sure a lot of loyal users would be happy to get this back.
Updated on 2018-12-23
A similar idea has also been suggested here:
Please vote for it, and add a comment there, so it may be considered. Any update on the matter should be posted there.
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