Spotify has a lot to work on. Integrations with new devices is a big one. They recently added support for streaming songs directly on the Apple Watch but are still yet to support saving them locally to play offline if you don't have your phone. New required features like this are constantly popping up. As well as other infinitely big tasks like optimizing all of their server side software to support and ever increasing user base.
They could also work forever on making suggestions better. As well as new features like lossless audio coming up soon. Supporting new iOS and android versions/features. There is never a point where a piece of software is simply done because the OS changes how things work constantly.
The companies that just contract out for a tiny bit of work every few months end up with garbage software because no one really knows or understands the code so they just tack on bad patches until the system eventually crumbles. And every bank I have used does have a full time development team. The one I currently use sends out monthly emails for the new features they have released and has a road map showing what they are planning on adding.