IMO, the dearth of carbines in the newer S&W "X"-frame cartridges has as much to do with dimensional issues as it does with handling the extremely high pressures they generate.
IIRC, both the .500 and .460 are long enough OA to pretty much preclude running them through a M-92 or Marlin M-94 action, while the .454 Casull isn't.
Both of those actions are relatively strong, but with operating pressures at or near 60,000 CUP the S&W rounds probably far exceed what either could be made to handle safely on a regular basis, too.
A "beefed-up" 336 action might not either. Even the .450 Marlin stops a good deal short of 60K CUP, and it's about the most potent thing ever offered in a production LA carbine or rifle that I've ever heard of.
Since the market niche for the big S&W handguns is so narrow, I doubt that there's enough potential demand for a "companion carbine" to justify the expense of designing and manufacturing an entirely new design for the breed.
There are several revolvers offered in the .454 Casull. Ruger, Taurus, Freedom Arms make at least a couple of models each. Compared to the "X" frame S&W's they all appear relatively petite to me.
IMO, your most practical caliber option in a sidearm/carbine combo right now would be the one you mentioned: .44 Magnum. I don't know for sure if the carbines can feed some of the newer heavy bullet loadings well, as OAL is critical and there isn't a lot of leeway in the design envelope to play with.
IMO, practically speaking either would serve your purposes about as well. You'd have more options in both revolver and carbine with the .44, and full-goose ammo might be a good deal easier to come by for it in most places.
Both have about the same effective game weight and range limitations and, within those, I doubt that most creatures could tell much difference given similar bullet mass and placement.
If the most likely predators to run into during the course of my daily life had two legs and/or generally weighed-in at under 400 lbs, I wouldn't feel too uneasy armed with either weapon in either caliber.
If I had to go somewhere that running into something with the size and proclivities of a grizzly was more than a remote possibility, I'd carry the biggest, baddest revolver I could tote AND an 1895G/M - both loaded with the stoutest ammo I could handle.
And if I could only take one, it'd be the carbine: every day, every time. In that kind of situation, my psychological comfort is gonna trump my convenience and physical comfort, period.
YMMV. Big bears don't live where I do, and I don't go where they do, so it's easy for me to hypothesize.
