This was what the Chimaeric Demons' Metal Fur brain crystal power did, albeit it didn't create plaques. The ability depended on hairs, but the base capabilities relied on such a mechanism.
However, Brain Crystal's powers conjuring armor up were more rare than that. This guy's, Gwen's, and Erik's own Force Bastion were examples of that.
This didn't mean they were impossible to kill. Sure, wounding them with conventional means might be hard., but there were other ways. For example, unless their armor had some kind of environmental resistance, they could still be drowned.
