I have no idea why stainless tubes were offered, or, why they went away. But, offered they were. I imagine pitting in the bores wasn’t a thing with stainless, but, don’t know for sure. Bet they are tough as hell.

Hard plating a surface gets you no more impact resistance than the base metal features. I don’t believe hard plating would help in a situation where the barrel steel was softer than steel shot an owner might put through it, for example.

Best,
Ted