If there ever was a gun with a truly, continuous taper from chamber to muzzle, the effect would be as no choke(cylinder). If there was a continuous taper from chamber to the beginning of the choke taper, only the last few inches of bore, leading up to the choke taper, would matter.
I agree with Jim that a full length taper would most likely act as little to no constriction. I've yet to find a full length taper barrel for testing. I do have a 7" taper full choke that acts as a full. As above, I do believe that the diameter immediately in front of the constriction is the controlling diameter.
