There is a previous idea that was replied to incorrectly by Spotify - Idea 137915. The point of this request and mine is to support the ability to add podcasts by URL when a podcast is a premium (paid for) subscription.
Like the original poster, I too have a podcasts that I pay to access without commercials and with extra content. Other applications allow users to add the url of the subscription directly to the podcast list.
It would be very useful to have all of my podcasts and music in one app.
Update: This idea has been reposted here.
Updated on 2018-11-20
Your idea was submitted a while ago and unfortunately didn't receive the amount of kudos needed to stay active in the ideas board (100 Kudos per year).
In order to keep the Ideas Exchange clearer I'll close this idea for now, but this doesn't mean Spotify rejected this idea.
If you think this is an idea which needs to be implemented, you're welcome to post it in slightly different again 🙂
Have a nice day!