Today’s WSJ piece on Apple talking with TV suppliers seems like the most solid evidence we’ve had that there might actually be an Apple TV coming down the tracks at some point. Yet I’ve been reasonably persuaded by many of the Apple TV skeptics that an actual television set doesn’t really jibe with APPL’s economics. I’d be very interested to hear someone smart (like Megan McArdle) walk through the various business challenges the TV market would represent to APPL. The rough list, to my mind, goes something like this:

* Most of APPL’s products are intended to be replaced on a semi-regular cycle. They want you to buy a new iPhone (and iPad) every 12 to 24 months and new laptop/desktops every 24 to 36 months. To that end, they have an aggressive product refresh cycle adding new features and designs every year or so. And they’re able to do this in large part because APPL customers are able to take advantage of a brisk secondary market for used products which defrays the cost of upgrade. You can afford to buy the iPhone 5 because someone on eBay will give you a few hundred bucks for your iPhone 4s.

I wonder what the typical TV replacement cycle is for an American household. My guess–and it’s nothing more than a guess–is that it’s a good bit longer than 36 months. If APPL jumped into the TV market, could they make the economics work on a longer product cycle? Or are they dependent on needing repeat buyers to help lower their manufacture and R&D costs? Or would they try to lure consumers into replacing their TV sets as often as they do their cell phones?

* How would consumers react to an Apple TV set if it was going to be refreshed and improved annually? Would they take to replacing their TVs more regularly, or would it prompt them to postpone purchase because they’re afraid of missing a key feature set in the next iteration?

* Would their be a secondary market for older Apple TVs, or does shipping large-screen panels make this a less attractive option for secondary buyers?

* Those are the hardware questions. From a “software” perspective, the biggest challenge would seem to be untangling broadcast rights. If the Holy Grail of an Apple TV is making channels and/or individual programs something like apps, which you purchase and then consume as you go (and this is a giant assumption), I can’t see how APPL achieves that without unbundling TV packages.

* A la carte channel subscriptions have been The Dream for a long, long time. But instead of moving toward an a la carte system over the years, we’ve actually moved further away from it. Sure, you’d rather only get the 30 channels you really want from Comcast–even if you had to pay almost the same amount you’re now paying for 500 channels that you don’t want. But from Comcast’s perspective (and the perspective of the media companies which own all of those channels) they’d much rather force you to buy the bundle. Their entire business model is based on bundling–forcing you to buy the little-watched networks if you’re going to get the most-watched networks–because it gives them more platforms and space for advertising. Time-Warner, Disney, Viacom, et al, know their business. It’s not clear what APPL could possibly offer them to make them begin to abandon it in favor of a model which would primarily benefit APPL.

* And if an Apple TV didn’t break up the bundling model, then what could it really offer consumers that the Apple set-top box doesn’t already give them? A better UI? TIVO on steroids? A TV panel that does Facetime? I’m not sure how much value there is to be added if the underlying economic systems of cable and advertising stay in place. In a strange way, the xBox is basically doing all of this stuff already. APPL could almost certainly do it better. But they don’t really need to actually be selling the panel if that’s the scope of their ambition.

Like I said, I’d be really interested in smart thoughts about this.