Why do you still have MPRIS into your client ? It never worked correctly and you don't care anymore. Do you think all Linux users are free accounts ?
Missing features are sad but we can understand, you do if you have time. But broken features (essential properties missing) for years is really not cool.
You can send length, title, artist, even thumbnail picture, but you can't send position ??? Why ??? Where is the hard thing you can't do in 2 minutes ???
Need programmer's help ? I can help, tell me. But do something, please !