As some have already mentioned, having a CD key /w a one time only online activation (not sure if GOG.com would support such though) should not be any problem for a boxed version. For me personally it would be a huge bummer if I now pledge but the game would only be available with Steams online DRM even with the boxed version, because I do no longer use Steam over 2 years now after it constantly blowed its chances with me.
However, while a local distributor might want to have some kind of copy protection enforced on the medium in the box, he certainly cannot dictate whether or not you can also publish it on GOG.com, can he?
I am eyeing with the KING Edition right now and for that I am more interested in the physical goodies, like the action figure, art book, making of etc. and having something of value decorating my room and something to wear, the physical copy of the game however is of very low value to me and a GOG.com download would have much more use.
But I think, regardless how this plays out, I will pledge for that KING Edition anyway, just for the goodies and knowing I supported an Idea of a game that deserves to get real.
These are my 2 cents