Oh, brother. Not only are televisions not alone as the sole electronic device in the room, they are not alone with a single viewer. Dad does not want Kevin to yell "SpongeBob!" while he and his buddies are watching the wide receiver head toward the end zone. If Apple returns to the TV set business, then we can expect Siri to play a role. However, it will not be the end all and be all that so many fans seem to think it will be.
First, I'm in the camp to think that a Siri (microphone) implementation is going to be in a very simple remote rather than the TV or next

TV. Thus, "Kevin" won't be able to flip it to Sponge Bob anymore than he can in the no-Siri world of TV remotes today. The gatekeeper is the person holding the remote.
Second, whether I'm right or wrong about "first" there are a ton of ways to deal with THAT problem. For example, after tuning to that game "Siri Lock until 4pm" to basically put Siri to sleep from any actions other than "Siri unlock" (and maybe "Siri mute") and then some form of override password to return Siri to normal functionality.
I do agree that Siri is not THE feature. Else, it appears that Apple may be last to that particular party. Personally, in spite of a rumor about an Apple Television about every 18 seconds

, I'm still skeptical about Apple getting into that particular business. Margins are too thin. Apple choosing a "perfect" screen size for all won't work as well as it has for other Apple products (but aren't we looking forward to the evangelists offering elaborate justifications how the sizes other than what Apple chooses for us make no sense for anyone... "99% of people don't need sizes other than THE size our Lord Apple has chosen for us" and maybe even someone will make a oft-referenced chart that implies that sizes other than what Apple has chosen make no sense for what our eyes can see, etc). Plasma vs. LCD vs. LED vs. something else? Ports? Locked down like an

TV or much more open (to all other video tech hookups) like all HDTVs available now? Etc.
And, most importantly, unlike the "revolutions" in computers, music players, phones, tablets, if an approx. $100

TV is also available to bring the software advantages of an Apple television to anyone else's TV, I just don't see the hardware being able to be enough to woo more than the most dedicated fans. More simply, Apple's successes are all built upon a locked-down merger of hardware & software. In this particular case, Apple endorses the software being separated out from the hardware in the form of an

TV box. If OS X could run on any computer (in an Apple endorsed way), would we all be as quick to buy Apple computers? If iOS could run on any smart phone, would we all be as quick to buy only Apple phones?
If an

TV brings the same software and unique hardware advantages to any television brand, it means Apple is endorsing a way for us to choose any screen size, any type of television (plasma vs. LCD vs. LED, 3D or not 3D, 1080p or 720p, etc), etc- including the HDTV
we already have- and still get the exact same (software) experience. Odds are high that Apple won't make their television panel. So the exact same picture would probably be available in an LG or Samsung, etc-branded television for probably about 30%-50% less. Spend the $100 or so for an

TV to incorporate the Apple software goods and save 20%-40+% for the EXACT same television screen. Or get the size & type of TV you really want and hook up the little box for the EXACT same Apple software experience.
If Siri is the big "I cracked it" benefit, that is mostly software. It will work in a next gen

TV (it would work in the current gen

TV with a software update and a new microphone remote). As many people have pointed out in many other Apple television threads, any big breakthrough feature that is software-based can be done in an approx. $100 set-top box.
Apple doesn't have to build a whole television to roll out breakthrough software benefits.
I'm in the camp that a true "I cracked it" breakthrough involves some kind of massive change in how the content is packaged for us consumers. Maybe it's some form of bypass-the-middleman (cable, satt) players though I caution that those very same middlemen usually own the pipes through which an Apple replacement solution would have to flow (so that ain't happening).
It's not the oft-stated "al a carte" as it's imagined, meaning "I pay $100 for 200 channels but only watch 10; so I want to subscribe to my 10 for 50 cents each". The business model that pays all the people to create the programs on our favorite 10 or so channels doesn't work if the average revenue per subscriber drops from $100 to around $5. Instead, the al-a-carte fantasy would probably result in many individual- but more popular channels- costing $5 to $10+ each to maintain the average revenue per subscriber (which, in part, would keep the creative infrastructure- the many people who actually create the shows- in place). Cut that revenue by upwards of 95% en masse and you better be ready for the replacement model to be what we get on youtube and similar where the no revenue/low revenue model for creating the shows actually works good enough to motivate show creation.
The "I cracked it" breakthrough probably requires some kind of new model of
distributing content that links Apple iCloud directly to iUsers without data flowing through Comcast/Time Warner/Cablevision/et all pipelines (and this will need to solve the local original content and live sports issues as well). It can't be a 2G/3G/4G wireless solution for both cost and finite wireless bandwidth issues. It would have to be either entirely new transmission technology or news of Apple buying out probably DISH network (though that's only a U.S.-based solution).
Look for rumors about Apple being able to link us directly to iCloud and then we'll have something. Until then, there is no cable-killing solution for the masses if those masses must retain a subscription to broadband from the same cable company (price of bandwidth would rise to make up for the defection of cable customers).