My train of thought is this:
if you want to cerakote outside of the body, to make it more scratch resistant - yes, a much more eye pleasing alternative to bedliner.
Add what ever little trinkets you have attached on the outside to that list.
Frame and suspension components on other hand, this is where my "why" comes in. Anything that is susceptible to be blasted by particles picked up by the tires, is literally a matter of time before will need to be re-coated again.
Regardless of what you spray you axles, bumpers or skid plates with, it will equally scratch off as soon as there is impact or sliding over hard surface.
Bonus to corrosion resistance can be put under question too. It takes years in shitty conditions to eat through thick metal.
There are so many things on the market at this point, that everything can be divided into two categories:
Works good and will last roughly as long as other good products.
Works bad, and will fail roughly as fast as other bad products.
Id gladly cerakote my carry pistol, it sees plenty of wear, salty moisture, and layer of coat will not interfere with functionality.
Same thing for AK that is made out of stamped sheet metal.
See no point in wasting it on aluminum parts.
Few layers of bed liner will do and last just as long on the bumper and other parts, and will preserve them just as long with equal amount of care.
Nothing against it, i simply see 0 sense in using it in this application.