It's probably less than that. It just doesn't seem worth it for Nintendo to make a separate CPP for a revision when the alternative for them internally is to pretend a built-in right circle pad isn't there (if they're against using it).
That's what I'm thinking. There are several reasons why I would seriously bet money the CPP is going to be in a future revision.
1) The original rumor of the CPP said that it is, and since that rumor has already been proven half right with the attachment, what reason is there to doubt the other half?
2) Like you said, they would have to release a new CPP attachment for any revision, so its easier to just include it anyway even if they don't plan to use it.
3) I think its part of Nintendo's long term strategy to position the 3DS as an optional controller replacement for the Wii U, and as we've seen at E3 last year the Wii U's tablet controller has dual analog, so that means in order for the 3DS to serve as a fully functional Wii U tablet replacement it also needs to have the same buttons/inputs. The CPP attachment adds that, but its more ideal to just have it integrated by default.
So for those three reasons I would bet money on it because I think its a safe bet. The only thing that's hard to understand is why dual analogs weren't in the original 3DS model? Obviously someone goofed up. Maybe things were rushed... I don't know. But it looks like Nintendo sees they made a mistake and are trying to remedy it.