IIRC stainless isn't actually rust proof, especially in applications where there is a lot of interaction with odd chemicals and things like sea water, so bridges may not be an ideal use for the product.
I have heard the same. Actually making rusting proof stuff is very hard. Specially if there is any chance of things like acids being involved. Coatings could help, but even then why not just paint regular steel.
Now other thing I wonder is how structurally sound some of the stainless alloys are? Do they have similar characteristics to steels now used?
IIRC, Coated rebar can actually fail faster or in less predictable and therefore worse ways. The coating is often damaged during install, but even perfectly coated bar forms cracks eventually. The entire system's galvanic potential is focused on these small exposed areas, causing extremely fast rusting. The coating tends to fail in higher stress areas, which means that not only does the bar fail, it fails in the worst possible locations.
Don't confuse stainless steel with galvanized steel. The latter is just normal steel dipped in melted zinc, once you're past that thin coating it'll rust just like normal steel does.
Stainless steel is an is an alloy, you can saw apart a beam made of stainless 316 and the inside will be just as stainless as the outside.
Now other thing I wonder is how structurally sound some of the stainless alloys are? Do they have similar characteristics to steels now used?