It sounds like you are referring to the sprocket, rather than the sprocket shaft (which is already stainless).
IMO the current ("V2") sprockets and masts are superior to stainless sprockets. Although stainless cogs
are bullet-proof, the chain/cable can skip a link if not kept at the correct tension. The current glass-filled nylon cogs are almost impervious to that problem. The newer cogs are wider and there is a "master" cog that locks the chain in (discernible in the picture below).
Cog wear is not much of an issue. In the picture below one of these sprockets is new; the other has over 800 miles on it. Can you tell the difference? I couldn't either.
Stainless sprockets use cotter pins to mount the masts (rods that support the fins). These is simple to replace, but are subject to sudden breakage over time because the masts wobble slightly back and forth in their slot. Present threaded masts will not wobble or back out if properly installed and should be reliable for over 1000 miles unless they've had multiple major bends.
Finally, if you have an unforeseen problem, current parts are more likely to be on hand at our local dealer whereas the older parts would likely have to be ordered.