After weeks of rumors, it seems nearly certain that the new iPod nano, debuting Tuesday, returns to the vertical form-factor of the first two iterations, a reversal from the “fat nano” Apple debuted around this time last year. (Here’s the shot if you haven’t seen it yet.)

Assuming this is all true, the move seems oddly retrograde to me. Apple, more than most other companies, prefers — perhaps even needs — to present each new product as an evolution from what came before. A new iMac design isn’t just different: it’s thinner, or lighter, or more ecologically friendly, in addition to the usual speed and storage improvements. Most iPod iterations so far have followed this pattern. The second nano featured a more durable metal enclosure, its successor a horizontal layout that allowed for a wider, video-friendly screen. Other iPod updates have added a non-mechanical scroll wheel, color screen, and so on.

The fourth iPod nano appears to be moving backwards, returning to the visual style of the second model. It may be this year’s models will boast new functionality not apparent in the spy photos, and that such functionality may make aesthetic considerations irrelevant. But it’s hard to avoid the conclusion that the fat nano simply didn’t work, and that Apple was retracing its steps to a more successful and well-received design. (I won’t entertain the notion that the form factor was inspired by the Zune.)

The nano would appear to have come to the end of its road, at least in regards to its design. It’s time for something new.

It’s time for Apple to kill the nano.

From a normal business perspective, this would be foolish — the nano still sells well, most likely remaining the best-selling iPod model, as it has been since its release. The retro model to be unveiled this week will undoubtedly sell well and give Apple another successful holiday quarter.

But how different from the Apple of 2005, which was in the exact same position with the nano’s predecessor, the iPod mini. Ever fearful of being leapfrogged by a competitor, Apple saw the mini as vulnerable, and decided that if anyone was going to kill their top-selling product, it was going to be them. The mini was terminated and the first-generation nano appeared in its place. The audacity of the move was nearly as stunning as the player itself: with the 2005 holiday shopping season about to begin, Apple chose an inopportune time to roll out a completely new product, and many observers felt that the nano’s early supply issues would have been avoided (and Apple’s holiday sales better) if they had waited until the following year to carry out the switch. Besides, who in their right mind kills a market-leading product? It’s like some action-movie badass who carves his own chest before going into battle; Apple’s competition must have been both baffled and scared shitless.

Today the iPod touch is arguably Apple’s “flagship” media player, its sleekest, most forward-looking and probably most desirable. But for the majority of buyers, those with small music collections and a need for a small and unobtrusive (but still usable) player, the nano is the best choice. Apple needs to reclaim the functional and aesthetic leadership in this space, and show its competition it’s not afraid to throw the dice on something new, bold and innovative.