I might be tempted. Though I'm a very happy AppleTV owner anyway.
Right now, it costs $3 per HD TV episode. That's too much. My household would burn though $20-$30+ per WEEK just buying normal network programming that we watch. A $30/month all-you-can-eat plan would almost work, though I'd really have to make sure that all of the needed programming is available. Last time I checked, there were several shows that weren't on iTunes (though they would be available... elsewhere....)
One enormous problem, as others have mentioned, is sports. It's one thing to be able to buy an episode of "The Office", but it's quite another to be able to buy that NFL, NASCAR, or MLB event. If AppleTV can't offer live sports (and they currently do not), then there are a lot of people that can't completely dump their pay TV. Granted, a lot of professional sports can be had from the major networks via free OTA HD, but that's a bit of a pain if you live far away from towers or don't have any good antenna options.
If iTunes could somehow offer individual, a la cart sporting events *LIVE* then they'd have a home run (pardon the pun). Imagine being able to subscribe to all of your favorite teams' games? Commercial free?! That'd be pretty freaking cool.
But I don't see that happening anytime soon. Or ever.
