Everyone says they want one ('94/.45-70) But if you will compare the internal width of the '94 Winchester to the diameter of the .45-70 case head you will see the most obvious reason why it won't be done, it won't fit! Even if it did, if you wanted to load it to the usually accepted capabilities of the cartridge you would fing that it was less that enjoyable.
And for anyone who questions the .45 Colt as a viable big game cartridge, then consider this. A .45-70 loaded with the Lyman 457122HP over a full charge of FFFg does 1400+FPS for 1450 FPE or so. A .45 Colt from a 24" rifle (Marlin CowboyII) loaded with a Speer 300 FP and 23.8 gr. H-110/296 (yes, they are identical, not just similar!) does 1638 FPS for 1943 FPE from my rifle. Everyone I know agrees that the .45-70 is , without question, adequate for deer, elk, or whatever, so what is wrong with the .45 Colt which develops 17% higher velocity for 34% greater muzzle energy?
This isn't the first time I have seen people argue that the .45-70 is great while the .45 Colt is inadequate. I admit I would prefer the .45-70 with a 400 gr. or so bullet at 1600+ FPS for elk if given a choice, but I wouldn't hesitate a minute to use the .45 Colt if the opportunity arose.