Hint: When you run Renoise in windowed mode, the current song/file name is always visible. You just have to manually resize the window to fit your screen.
But yeah, in general it could be nice to also show this information somewhere when in fullscreen mode.
I wouldn’t complain for a ‘mouseover’ in the top row eg in the place of the VU meter. So that if you move the mouse there in fullscreen mode the VU will hide and the (full?) filename will show.