Could Spotify be purchased by Facebook? While Daniel Ek has publicly downplayed the possibility, a key investor in the company isn't ruling it out. Joakim Dal of Swedish investment house GP Bullhound, which holds equity in the company via one of its funds, says that while a Spotify IPO in 2017 remains "likely," sale to Mark Zuckerberg's social giant is still on the table.

"We think a U.S. IPO in 2017 is likely," Dal told Breakit (as reported and, thankfully, translated, by Business Insider), "but also don't discard the possibility of a sale to Facebook. Historically, building social networks around its offer has been a weak spot for Spotify. In that sense a deal with Facebook would be something positive. It would also make Spotify stronger against Apple, as Apple today doesn't have a social network connected to its offering.”

Ek and Zuckerberg are acquainted, Dal added, and if FB is ready to make a big music move, he could certainly afford the asking price; the expected IPO valuation for next year is $15-20 billion.

Spotify recently announced it had 40 million monthly subscribers to its streaming service, leading the field in an increasingly robust market. By the time of a projected IPO, the company is anticipating 50m subscribers, 100m users of its ad-supported free tier and some $5 billion in revenue per year. 100m paid users are expected by 2020, God willin' and the crick don't rise.

Visit the BI story for a "scenario overview" graphic with lots of numbers.

We love speculating, so let's say FB does buy the Spot. That means the biggest streamery and the biggest social engine are integrated, with the sharing component of playlists and other content kicked up to a whole new level—and social users afforded a new dimension of music discovery.

How would the subscription and free tiers be separated within a FB-controlled universe? Would this be better or worse for rights holders? Stay tuned.