The problem with supplying scale wheelsets with steam locomotives is in changing the drivers.
As I said i'm not a steam guy so it might be harder than most would want to tackle but I was thinking along the lines of the Glacier Park O scale locos where a set of P-48 wheels can be purchased with the standard O scale loco. If the manufacturers would rather stock 2 versions that would certainly be easier from a buyers perspective. I just would not want to them to only make high rail versions then claim S scale locos don't sell :> I'm glad it's a problem I don't have to worry about for freight cars where wheel swaps are pretty painless....DaveBranum