The cost of changing from 0.10->1.0 is likely less than having a wrapper?
Everytime a phonon backend does something 'new' that solves an existing problem - What happens then? You add API, and then all media players have backends that are subpar, or must media players verify if current backend supports the new feature? Either way the pain is just pushed to API users.
Or must every backend support a new feature before it's added? So everything slows down?
And how do media players handle support? Now they get to support problems from X backends instead of just one. Oh the mkv parser is broken in Z, but works in Y. Pain :(