I agree with the "Why?" there. I don't think it's in the realm of feasible engineering to design a revolver that both rotates the cylinder, cocks the hammer, pushes the cylinder forward to allow for brass to enter and align with the forcing cone, and then release the hammer in one trigger pull unless that trigger pull feels like dragging a sled down a set of railroad tracks.
On top of... you really don't loose much velocity between the cylinder/forcing cone gap. It's a moot issue. Case in point, I can load 125 gn .38spc with 3.8 gns of 700x. I can load a 125 gn bullet in 9mm over the same charge of 3.8 gns of 700x. I get only slightly more velocity from the 9mm, and the majority of this likely stems from the higher pressure rating of the caliber.
Also, if much was lost at the cylinder / forcing cone gap, revolvers wouldn't give extra velocity with longer barrels. But the do, so losses around the gap is not a major issue. If those losses are not a major issue, then there is no need for a rebirth of the Nagant (or at least any practical need).