I don't think we'll ever see a NEF rifle in .454 Casull. The working pressures that it operates at are way too high for the NEF action. Some people will point out that it is chambered in high pressure cartridges like .308, but the actual chamber pressure is only part of it. With large diameter cartridges like this, the stress from bolt face thrust is usually the limiting factor. I have heard of problems with these guns showing pressure signs with the .243 and .308. The .22-250 model was apparently discontinued for the same reason.
The Marlin Firearms board has tons of posts from people who for some reason want a .454 lever gun, and just as many responses that say the same thing about pressure/ bolt thrust. NEF has suggested that the Handy-Rifle action is about as strong as the Marlin 1895SS, at least in its .45-70 variety. While the .454 is smaller at the case head, its pressures generally run much higher.
I think they might be able to build one capable of firing lighter .454 loads, those with less pressure than the factory loads, but I can't imagine a modern manufacturer that would offer a gun that is insufficient to handle even SAMMI factory spec ammo.
Unless one was trying to put together a .454 rifle/handgun combo, I don't know why we would need a .454 Handy rifle, or lever action for that matter. The .45-70 will do anything the .454 will do and more at pressures which are tolerable to the NEF. A warm .45 Colt will in a rifle length barrel is also very capable.
The .454 Rifle route pretty much limited to the TC Encore, the Browning Hi-Wall, and custom Ruger # 1s.
