Call me a pessimist if you want, but I don't think these console additions will be successful. Sure, there's a lot of hype surrounding them right now, but even still I remain dubious of its success. (Well, Microsoft is going all out - read: batshit crazy - even if Sony hasn't been pushing nearly as hard as it ought to.) So I've decided to muse a bit on why I'm not feeling it for Move and Kinect.
(Note: this is meant to be separate from my own personal feelings, measuring success in monetary terms. Meaning, I know right now that Kinect and Move are not for me. But I can muse about how well Call of Duty: Black Ops will do, even if I'm not interested in the game itself, can't I?)
Now, no console add-ons have worked in the past. Sega CD and the 32X are the poster childs for this (mainly because very few people have had the guts to try again, and for good reason), but more to the point it's not because the hardware or even software "sucked". It's because they're dividing their marketbase.
So let's look at, say, the 360 right now. We can divide them into two groups, "people who own a 360" and "people who don't own a 360". Who do you sell Kinect to? Well, among people who own a 360, assuming the price points are accurate, Microsoft is pretty much trying to sell them a whole new system for $150 - that's three-fourths of the price of the Wii, and not exactly a small number. And that's for a fraction of the market - among people who don't have a 360, you're trying to sell them this new system for $300 to $400, and most of that cost is a product they've already decided not to get for one reason or another. The difficulty to overcome is much more difficult than just trying to convince people to buy a 360 in the first place, because they're appealing to people who already chose not to buy the system sans-Kinect at a lower price point.
Speaking of price point, Move is going to be annoying to the consumer because you get it piecemeal. Sure, if you have the PS3 and the PS Eye, then you can get into Move for the very nice price of $50 (plus games), but for a full set of nunchuck-analogue plus a second wand (since some games will use two wands for one person), that's $130. Without the PS Eye, it'll cost $180 and even that is assuming you own a PS3. It's $400 (or two Wiis!) otherwise.
Furthermore, price is a huge deal. If Microsoft and Sony weren't competing directly with Nintendo, they sure are now. And Nintendo is the king of the price right now at $200, which is beat by the already-invested prices of $150 and $180 for a full one-player set, but that's incredibly close to where the Wii is at. And then for people who aren't already invested, it's pretty clear where to get motion-control gaming from, and it ain't Sony or Microsoft.
This is assuming, of course, that the average "casual gamer" knows about Move and Kinect and their above prices. It is my experience that the average person hasn't heard of the PS Move, and when described to them they immediately liken it to the Wii (which right now is a household name, like Xbox and Playstation); and if people haven't heard of Natal (now Kinect), they liken it to the "Eye Toy" when described to them. This is real bad. No one is going to pay twice as much for a Wii-analogue or about four times as much for a next-gen PS Eye. Microsoft at least has been bending over backwards in clown shoes to get peoples' attention. Right now, there's as much excitement surrounding the Move as there was when the PS Eye came out with Eye of Judgement, and we all know how that turned out. (The two situations are also disturbingly close since Sony was awkwardly trying to take a piece of the incredibly lucrative CCG pie.)
So right now I'm not expecting either Kinect nor Move to do well. That isn't to say that some people won't get excited about them (or that others will declare them a detriment to humanity), or even that they will make a profit in the long run, but right now neither is poised to tackle the admittedly difficult challenges ahead of them.
Microsoft and Sony, prove me wrong.