DeaDBeeF already has both GTK and Qt UI plugin options, so just use the one that’s most native to your desktop (GTK: GNOME/MATE/XFCE/Cinnamon, Qt: KDE/Trinity/LXQt). If those UIs aren’t sufficient for some reason, since they’re plugins they can be forked and tweaked or if one was so inclined, they could write a whole new UI plugin. No need to wait on the author.

And while it’s true that Qt fits into a GTK desktop better than the reverse, I still find myself preferring using apps written with the toolkit that matches the desktop in both cases.