I wont say I know how Spotify works as a business, but currently I see it in this way.
Spotify, in actuality, has two different app structures in the Windows platform. Both of which have deal breaking differences to each other that make it very diffcult to make a universal app that works on Desktop and Mobile. The two apps found on Windows are:
Desktop Spotify (Spotify Desktop Client for Windows 7, 8 and 10) that works predominantly with a mouse and keyboard. This app has lyric sync with Musicxmatch, that allows people to save playlists offline, but not individual songs, albums, or artists. And..
Mobile Spotify (Spotify 5.0 for Windows Phone) that works predominantly with touch. Different and simplified from Desktop Spotify, this app allows people to save not only playlists, but songs, albums, and artists as well, whilst removing lyric sync.
Currently, the problem with Spotify's stucture is that their premium accout only allows 3 devices to save content offline and those three devices includes both Desktop and Mobile. So that means
I can save offline playlists only on my 1 laptop, and
I can save offline playlists, artists, albums and songs only on my 2 mobile devices, in my case it's a Windows Phone 8.1 and an iPad Air.
In order to make a universal app, they need to rethink how they will treat devices with these apps: Are they mobile or desktop? What type of music stucture (playlist, albums, artists, songs) will be allowed to save on these devices? What does this mean for the x86 Desktop app that has already has a lot of secondary features such as Musixmatch lyric integration?
Because of how Spotify has structured it's app in agreement with Music Licences to stream music in a particular fashion, it's very difficult for Spotify to warrant making a Windows 10 universal app when they already agree to do certain things with the music.
At the very least, however, they could improve the current windows mobile app. Things such as...
Jump lists for long lists of atists in my music
Better background management of offline content.
THE SHARING FEATURE IS STILL A MUDDLE!! Unlike iOS, Spotify for Windows Mobile still only allows sharing to individual apps and not to all social media apps.
Nifty integration to other apps on the platform: such as Shazam and Musixmatch, that I can understand if it is a long, arduous argument but it is possible.
Preview Music by holding down a song, a playlist or an album.
Spacing in the hamburger menu
Things that I hope they will not mess with
Album art in Artists view on my music
"My Music" in of itself, the ability to save individual music is great!!
Basically, what they are doing right now. They made a good app for Windows Phone, but it needs more, not less.
I'd just like to have an official update to be fair. Are they or are they not going to be supporting Windows Phone with an universal app going forward? An update to the Windows 8 app has been far, far overdue and would probably be irrelevant at this point.
I can't support Spotify with a subscription if they don't support my mobile.
Yeah, I get where you're comming from... Mostly because sometimes I would wish they had more to the App they have right now because would be missing a feature, or getting frustrated with quirks that seem to be easy fixes for developers but they have decided not to look into it.
As for what Spotify is doing, they can't say. I swear they fight the losing battle of the freemium/premium and that takes up more of their efforts and takes them away from even thinking about support but that's just opinion. I hope my $12 per month is doing something good.