As some others have already alluded to, its worth keeping in mind that we have one, rough drawing of Sears' knife. And that no one has found the actual knife that he used. We have no technical data or precise measurements of length, thickness, etc. So all "Nessmuk" knives are really just guesstimations and interpretations.
Thus, the Nessmuk knife is an idea, not a strict design. As has been noted many times before, Sears likely didn't use this knife for much wood processing - he saw it as part of a well-rounded trio, with other tools to more likely do the bulk of the woodwork, and this knife used for a variety of other camp tasks. With that said, one advantage I see from my totally amateur point of view, is that a blade of this depth and shape has the capability to be a remarkable slicer, and have enough spine for other, burlier work, if given the proper geometry. In other words, it's possible that modern tweaks to the Nessmuk could yield a more versatile, stand-alone knife, without detracting from the historical underpinnings of the original idea.
I know this may sound like sacrilege to some, and there are those that would counter that there is no need to tweak the original design (whatever it might have actually been...). But I'd also put forth that while we have put George Washington Sears on something of a bushcraft "pedestal," we also need to remind ourselves that we actually have a very limited window into what tools Sears used, based on one drawing (and brief mention in his only book), at one point in time of his life. Who's to say that a few years after writing Woodcraft he didn't change this design, or hit upon something else that he liked more, but that he simply never get around to documenting? And so while it may be tempting to latch on to a fixed moment in history, its worth bearing in mind that all things evolve, and that our scant factual data of this one design doesn't mean Sears' knife wasn't something that couldn't still be adapted and improved - either by himself as he continued his life in the outdoors, or by others afterward.
After all, as someone much smarter than me once said, "Tradition is not the worship of ashes, but the preservation of fire."