I believe Spyderco has already perfected the Chinook as a folder.
I see no way of improving on absolute perfection.
The Chinook IV, then, ought not fold.
Make it fixed, and when I say identical to the II and III in every respect and nuance, I even mean the little the scallops in the scales on each side for guiding the thumb into the hole.
Identical in every respect and nuance means retaining the hole in the exact position and conformation as in the II and III.
In fact, I'd even use the same scales and liners, with the same cutout for the lock release in the scales, as sort of an insider's understanding of the Chinook's roots.
To me, the real challenge would involve designing a multi-position sheath that would retain the knife and, at the same time, deliver it quickly to a defender's hand, ready for action.
This same sheath, then, would accept and carry a Chinook II or III in its opened configuration.
Spyderco could sell the sheaths to people who own Chinook II's and III's.
For myself, though, I could not live without a fixed blade Chinook IV that had an IWB sheath for the blade portion of the knife, with the entire grip exposed above the waistband for instant excess, and with some sort of extension of the sheath to act as a liner between the grip and the body to keep the grip from rubbing the wearer's skin through his shirt.
A very high-ride sheath.
Additionally, I would like to see a sheath I could take apart and put back together as a mirror-image of itself, so I could carry it on the left or right side, and so I could carry it so oriented as to present itself in either the Ice Pick grip or the saber/hammer/baseball-bat grip, depending on the wearer's hand and grip preferences.
I would skeletonize the tang of a fixed blade Chinook to exactly match the skeletonization of the present liners, and I would use the same liners between the scales and the tang as the present folding Chinook uses.
I'd also stick with S30V.
Make a fixed blade Chinook IV as indistinguishable from its folding predecessors as possible (I'd use the exact same screw/fastener pattern, and even the same fasteners), and put the thought, research and development into the most flexible, multi-position, left/right, IWB/belt sheath the world has ever seen.