My point is that josh mentioned some time ago (I think on his tumblr, or twitter), that he is not sure yet whether you should decide on a multiclass at character creation, with a fixed progression throughout the game, or if you can just take levels of a second class whenever you want.
Just to be clear: the first option means you advance in both classes equally (think dualclassing of AD&D / BG), while the second option means you can decide each lvl which of two classes to take (think multiclassing of D&D3.X / NWN).
My impression was that he described the first option in the IGN interview, which seems like a huge loss in build diversity (I'd actually prefer that, since it would probably balance the dual classes much much better).
Maybe he was toying with implementation ideas at somepoint?
As far as I know though, the second option you describe is how it is going to be in Deadfire.
The question that remains for me, is more of a usability issue. Will they lock you out of multi-classing if you disable it? I know not the official word on this at all, just going by what I'm hearing here. I can trust myself to keep the multi-classing option open. I'd just hate for other players to get locked out of the option because they at first think they want to roll a pure class. Of course I can see the opposite issue happening were someone feels compelled to pick up a second class only to find it's not working for them. I guess you can't protect the player in the end.
A think as long as I can defer picking up a second class until way later I'll be most happy. Though I think I may have read you have to at least pick up that second class at level 2 or something... not sure...