Man, I'm still so thrilled with the EU getting Spotify rather than Slacker. I've been sitting here trying to stump it with obscure Icelandic band after obscure Icelandic band, and only succeeded once (
Wesen, the short-lived side project between Júlía from
Oyama and Loji from the defunct
Sudden Weather Change). I mean, they even have
asdfhg. - a band literally named by mashing keys on a keyboard.
I wonder if the US will be lucky enough to get Spotify at some point? Or maybe there was some sort of licensing problem?
I'm hoping as well, but I think it is just hope. I'm not sure why they chose Slacker, but my guess is cost -- Spotify is number one and they know it. They have no reason to cut Tesla any deal and Slacker is "good enough".
Now, I've been surprised at Slacker's coverage. I'm not as well versed as you on obscure groups, but they had someone I stumbled on, Bjorg Thorhallsdottir (pardon the missing accents, not on a mac

). My main issue with Slacker is also a problem with Spotify: missing minor groups and licensing issues.
For example, neither have Jupiter Hollow (no, not
that Jupiter Hollow, it was a midwestern band with AFAIK only one album published), nor Big Hat (no, not
that Big Hat, this one toured in the midwest, I have all three albums and was lucky enough to see them live), nor Rondellus (no, close names don't count -- one album,
Sabbatum, which is Black Sabbath translated into latin and played on medieval instruments). They only seem to have more recent songs from Muslim Gauze But outside of fringe examples, both have quite good coverage of even obscure bands.
The regional licensing bit is the other frustration as I rather like AKB48. There's
one album that is licensed for the west and is all you can get on Apple or Spotify (well, there's the Candy Rush song from a movie -- at least the album has been added). That's quite a bit of material that simply isn't available: I'm up to something like 35 albums+singles which gives fair but incomplete coverage of their song catalog. In my Tesla I can search for and find AKB48, but it won't actually play anything. Plenty of K-Pop, though.
But for someone with less fringe tastes within their authorized region both give excellent coverage and acceptable quality.