The whole slidepad add-on accessory is a Big F U to early adopters. It looks very awkward to use and it'll make the 3DS massive and unpocketable. Nintendo should have included dual analogs right form the beginning or not included them at all. I'm really disappointed in Nintendo. I regret having bought the 3DS last month.
Mobile gaming can't adequately replace dedicated game handhelds sure. But the mass market doesn't care about portable gaming enough to want to invest on a dedicated gaming device and $40 a pop on games. When I'm out and about, I don`t even bother taking my 3DS, DS or PSP with me. If I need to kill time, I just surf the internet on my Android phone or play games on it (right now I'm rocking Symphony of Eternity, a 16-bit era RPG for Android). My 3DS/DS/PSP stay at home and I play them at home.
Dedicated gaming handhelds are between a rock and a hard place in the west. On the go, carrying an extra bulky device around in addition to your phone is an inconvenience. And at home, most people would prefer to play on their home consoles than on portables (that's not true with me and many other gamers but this seems to be the case with the majority).
I bought a 3DS becaue I actually prefer gaming on a handheld than on a home console, I figured that it wouldn't get another price cut anytime soon and I had faith that Nintendo would deliver on the games front (right now I have only two 3DS games and these are the only two 3DS games I want to play. But in the near future more will come out.) After this whole dual analog BS though, I'm quite pissed. That slider add-on accessory doesn't look very comfortable. And if I actually do want to take my 3DS on the go, I'll need to put it in a bag because that monstrosity will be too big to fit in your pocket with the add-on.
Next time I'm just going to avoid being an early adopter. It sucks (that means I'm not going to jump on the PS Vita right away). I had figured that Nintndo would release a redesign in the future. But not with an extra slider pad. I thought it would have just had better battery life and maybe a slimmer redesign or something.