I know at least one shop was doing valve stems for a while in the '60s. How it worked, or whether it is done now, I don't know. Google Swain-Tech.
There are other surface treatments of camshafts (not coatings), such as Parkerizing. Also, any good modern oil has additives that stick to the cam to protect it from a dry start; you can feel it by rubbing your thumb on a cam when you pull it out of a motor. A new addition to the market is the ceramic-base lifter. These have very low friction against the cam lobe, so low-drag and very low wear, and they have no moving parts, an advantage over roller-tappets.
Also, if wear-reduction is your aim, install an electric engine-heater that you plug in at night. These are commonly used in cold winter conditions, but have numerous advantages in almost any climate. If Detroit wanted to build cars that last a lot longer than the warranty, they would have engine-heaters built in.
That's all I've got to say to you, Drift, and I'm getting myself de-listed from this thread. I can't even figure out some of your stuff, and even when I can, I don't like your attitude. You're either too lazy to edit yourself, or you think there's something cute about writing like an immigrant fresh off the boat. It shows a basic disrespect for the rest of us.