The Apple TV, Cupertino’s “hobby” of a set-top box, is often used to test out new fabrication process for the A-series chips that go into iPhones, iPod touches and iPads. The last Apple TV ran a 32nm A5 processor built by Samsung with a single-core disabled, which eventually ended up (in a dual-core capacity) in the iPad mini.

With the new third-gen Apple TV, Apple’s at it again. The new Apple TV is functionally and physically identical to its predecessor, except for one detail: it features a 28nm A5 chip built by TSMC. But what does it mean?

Reading between the lines, there’s a couple of interesting things about this report.

First of all, the chip was made by TSMC, not Samsung. That makes the third-gen Apple TV the first iOS product to boast a chip inside not built by Apple’s frenemy.

Cupertino is clearly testing out the waters here. As we’ve previously discussed, allowing Samsung to foundry Apple’s chips for them gives Samsung all sorts of competitive advantages over Apple. TSMC, another massive foundry, is a safer partner in that it is not a direct competitor to Apple.

However, TSMC has its problems as a partner to Apple: TSMC often has yield issues delivering new chips, and its wide range of clients means that Cupertino might not get the privileged client basis that Apple demands.

So a TSMC chip in an Apple TV means Apple is toying with the practicality of moving some or all of its chip fabrication over to TSMC, and is testing the waters with their hobby set-top-box to see if a wider partnership is possible.

The other interesting thing here is that Apple has shrunk the die-size of the A5 processor once again, this time down to 28 nanometers. That’s a big deal: the A5 processor started out in the iPad 2 as a 45 nanometer chip. That’s comparatively a beast, almost 40% bigger than the new chip.

There are a lot of practical advantages that come with shrinking the size of a chip. They become cheaper to make, for example, because you can fit more of them on a wafer. They also get much better power efficiency.

So here’s my theory. The 28nm chip inside the third-gen Apple TV is our first look at the A5X chip that we’re going to see power the iPad mini with Retina Display.

The difference between an A5 and an A5X chip is essentially that the A5X has four graphic cores to power a 2048 x 1536 pixel display, and the A5 doesn’t. Otherwise, they are identical.

So if Apple can make a 28nm A5 chip, they can make a 28nm A5X chip… and in doing so, the A5X chip would be much more power efficient than the one in the thid-gen iPad, which required so much power that Apple had to make the iPad thicker to accomodate the extra battery power.

Coupled with the possibility of the next iPad mini using a Sharp IGZO display, and the iPad mini with Retina Display could be just as light and power-efficient (if not more so!) than the current model.

Wouldn’t that be something?