What is PureOS and how is it built?

There are a few things I wonder about this article, but it sadly hasn't a comment section. In case anyone from Purism is reading this:

Does this mean PureOS (and thus librem 5) will be on purpose biased toward 100% free software system (my experience with debian is that while you can run non-free sofware on it, it's made more difficult than it could be)? I'm especially worry about this : does this mean it will be difficult to install spotify-linux on librem 5? Spotify is an important part of my mobile experience, I wouldn't want to sacrifice it.