According to MIDA Research (via Digital Music News), as streaming cannibalizes other forms of music sales (eventually growing 238 percent by 2019), download revenue will decline by 39 percent (only 5 percent less than the rate CD sales will fall).
From MIDA Research:
“23% of music streamers used to buy more than one album a month but no longer do so. Download sales are affected most and will continue to feel the pinch with 45% of all music downloaders also music streamers.
Thus although streaming and subscriptions will grow by 238% on 2013 levels to reach $8 billion in 2019, download revenue will decline by 39% – only five percent less than the rate at which CD revenues will fall – leaving streaming and subscriptions representing 70% of all digital revenue.”
Much of this is attributed to the fact that the “first wave” of subscribers to streaming services like Spotify are/were among the most valuable iTunes downloaders.
In the age of streaming, downloading has just become an inconvenience.