It's true. There will be no such thing as a single-use device dedicated to playing digital music in 3-5 years. You should save up your old iPods and Zunes (RIP) and keep them in nice working order for the folks that will want to buy them on eBay in 2035. There hasn't been any significant improvements to the MP3 player market since the introduction of the high-capacity flash drive, 3 years ago.
The thing that stinks is that there is no current device that makes playing and listening to digital music 8-10 hours a day, a practical habit. Technically, you could use your phone. Technically, you could use your computer. And technically, you could use your tablet. However, none of these are good, mobile solutions with long battery life. Within two years, you (yes, YOU) will have a multi-dimension device that acts as a cloud-based computer, phone/messaging/email device, and as an entertainment hub (think tablet but smaller and multi-dimensional). There will be exponential growth in battery life over the next 18 months with the addition of energy-efficient processors and equipment architecture, giving these multi-purpose devices 7+ days of battery life, instead of a mere few hours. So if you're an MP3 player junkie, you'll have to tough it out for a while until everyone's future devices start arriving on store shelves at the end of 2012. And yes, I already miss the Zune.