True, but the DSi, with added online shop and a camera, didn't stop Nintendo from releasing it. The same thing happened to the Gameboy to Gameboy Color (added colors) and original GBA to GBA SP (with added backlight). What I'm trying to say is that if Nintendo should ever release an upgrade of the 3DS, it should at least have a second slide pad.
DSi Camera was a function that was used by a HANDFUL of games, most of which were download only.
Gameboy Color came out many years after the original Gameboy.
The backlight didn't make any new games incompatible with the original GBA.
A right analog stick is another deal entirely - it's an industry standard feature on console controllers, and would fundamentally change the way developers view the system. If we think it's unfair of Konami to make a MGS game that essentially requires the user to have the CPP, that kind of them would completely explode after a revision which included a right stick. Basically, you would absolutely HAVE to get the CPP or a new 3DS for a large chunk of software which was developed after the new model.
I'm not saying it *won't* happen absolutely, but I am saying that I think it's unlikely, and that's my reason why.