It was bound to happen sooner or later. It was an interesting line of products to have as an alternative to the iPod Touch. I've owned an older iPod Shuffle and a 5th Gen(?) iPod Touch. I personally prefer the iPod Touch mainly because I can see what music is next or if I wanted to listen to something specific I can do that easier with an iPod Touch than the iPod Shuffle and I can do plenty of other things besides listening to music on an iPod Touch.
Apple is definitely one of those companies that tries to set trends so I wouldn't doubt if they already had a plan to introduce something else or just stick to a streamlined product lineup .