Do not give too much control over a single industry to a single corporate interest. I am a netflix subscriber splitting a 4k account 4-ways, but I have absolutely no doubt when they have the market they want, the only way they are gonna keep investors interested, the 3rd-party studios low-balling prices, or their own production assets happy with their salaries is by breaking the current service in some way. It surely won't be ads, but I'm betting 4k or even HD will at some point increase to become prohibitively expensive for a big chunk of their user base that currently has those and people will have to compromise. (it already increased in the past). Either that or the account-sharing capability will be cut-off.
Subscription services have flat rates, and when the user-base stops growing and also becomes flat while you have already optimized your entire business process, the company freezes financially, which is also known as stagnation. If you look at other industries that have peaked, such as ISP and other communication providers, you know exactly what happens: they increase prices, decrease quality, or bundle useless services to artificially raise prices. And these guys have competition to cope with, while Netflix is like Apple and Android ecosystems together, while Hulu, HBO Go and whatever else are like Windows Phone. It's not gonna be pretty when it happens.
And... Spotify is gonna be just the same, with the difference the music industry provides a infinitesimally cheaper product (music production is almost free when compared to film/tv) at a much higher end-user cost. Spotify knows they have a high-margin, "premium" feeling product and they don't sell it cheap. There's a reason they are so restrictive with family plans as opposed to Netflix account sharing.
Different industry example: Console games - just launched prices have risen from around 40bucks to 70 in less than a decade. Another industry: smartphones - top-tier flagships now cost more than 1000 dollars unlocked. The first iPhone fully spec'd out cost 599$ while top of the line 7 Plus costs 969$. 370 bucks is no joke my friends, apple needs cash to build that UFO.