As an older guy with hundreds of records and CDs who wants to keep building my own library of digital music but doesn't have to pay for songs I don't like to get the ones I want (figure it out), I'd be interested in a service where I pay a minor subscription fee ($10-25/year) for the right to stream an album or two at a time, so I can check out new music that interests me. Then pay maybe 99 cents per song for a decent DRM-free MP3 download for the songs I like and want to keep. A FLAC download for the snobs could cost a bit more per song.
I don't want to pay the larger monthly fees for today's streaming services because most of the time I listen to the thousands of songs I already have. I just want to be able to evaluate new music in a convenient and affordable fashion, and pay a reasonable price for what I want to keep.
Why stream albums instead of mixes like what we have now from Spotify and the like? Because that's how I evaluate music. Again, older guy. No reason the service couldn't do both, but I want the chance to hear everything from artists I'm interested in, not just the hit(s).
This makes sense for those of us who already have a music library, who were conditioned to the idea by the need to buy stuff if you didn't want to be at the mercy of local radio programmers. We've always been a minority, but we're the minority that invests time and money into the industry, so we would seem to be worth catering to. Does it make sense for the potential market of younger collectors with different habits shaped by torrents and streaming services instead of radio and record stores? I think so, but doubt the industry will ever get it together enough to let us find out.