I'd go for a re-issue of the 547, but why not add the option of a .38 Sp. or .357 conversion cylinder to go with it? Ruger sold a fair number of their Blackhawks with that option, and it's nothing S&W hasn't done before with the Mod. 53 and with some of their .45 LC/.45 ACP offerings. It was a while back, but I recall the reviews on the Ruger convertible Blackhawk found excellent accuracy with both 9mm and .357 ammunition.
I'm not sure about the idea of the .357 Sig in a revolver. It's a nice round, but probably not enough benefit to outweigh the difficulties. The history of the Model 53 illustrates the issues of shooting bottle-neck cartridges in a revolver. Granted, almost all the problems were traced back to people leaving oil in the chambers, but why ask for trouble. Bad enough to deal with the rimless cartridge extraction issues without adding in setback problems and the necessarily thinner chamber walls you'd need to accommodate the fatter rounds.