The ability to press a button on desktop version which will send exactly what you are playing to your mobile version and auto start up. Not sure if this is technically possible. But I think of the ability to go to Google's play store and purchase something from the website and then automatically download the program to your phone and install it. Without having to touch your phone.
But my idea would be I have an album I'm listening and I have to leave. So press a button (like play or pause) which gives you the option to continue song on your phone. Or pop up when you close the software if you'd like to continue on your phones when you go to your phone and unlock or boot up, spotifuggle will auto launch and a notification will tell you to press play, which will be right where you left off.
Like I said, not sure if this is technically possible, but it's an idea that comes in my head when I have to go and have to go and find what album I was listening to.