As a corollary to your point about paying money for a free service, I recently decided to help fund Riot/Matrix.org development on Patreon (currently $5 a month). Both are currently presented as a free service, and I recall them stating eventually they would have paid-for integrations and bonuses for corporate users, but predominantly most of the users are on the matrix.org instance using the free service. Needless to say though, it's been a damn good app / backend most of the time, and has made my life much better than before, when I would connect to a handful of various services to accomplish the same goal. I think the reason I didn't see contributing money to be as big of an issue, is that the work is 1) open sourced, which is almost as if I can have some part of ownership in it (don't take this too literally) and 2) I pay $5 for a vps to keep my personal website / email up. If I'm willing to part with $5 for email (which some days could be thought of as not helping my life), I might as well do it for another application / ecosystem I use everyday that does help me in many ways.

Overall I think that to an extent you can't just expect that most people will pay for something that would otherwise be free, or has been free for a long time. You end up gaining a bunch of users from the "lower pool" that will only be there as long as it's a free ride. But a certain class of users will pay for something if you ask for it, because it has made their life better in some way, and they want to ensure it continues in the future. There's an interesting parallel here to Craigslist / Kijiji, where most seasoned users will put a price on items they just want to get rid of. They do this because a very large portion of troublesome users who troll around for free stuff will outright ignore the posting. This actually makes it easier to get rid of things, because you don't have to deal with fielding fifty calls of people who might pick it up but then never show, or who just call you to ask if you have anything else for free that can go with it (and subsequently waste your time from giving unwanted items to people who will actually, you know, come get them from you).

It does make you wonder if the idea of a buffet-style, everything-is-free-forever ends up tainting the user pool, especially with regards to sites / applications that deal with art / multimedia. Sure, there's piracy out there, but companies like soundcloud don't really have the corporate backing behind them to scale infinitely for more users. Maybe from the outset they should have charged a $5 yearly membership or something. They may have had less users, but at least then they'd have something. Or perhaps I just don't understand their business model. Who knows?